Miu Fūrinji is a young teenage girl of average height. She has fair skin with a beauty-mark under her left eye, bright blue eyes, and long straight-blond hair reaching down to her hips with short bangs. Normally, she styles her hair to allow a few strands of hair to form a thick antenna-like strand hanging in front of her face. While constantly considered very cute and attractive, her most noticeable physical trait is her slender yet surprisingly developed and curvaceous-frame for a young girl, especially her well-endowed breasts. She also sports slim waist with flared hips, and a lean yet well-defined build.
Initially she would wear non-corrective glasses and braid her hair at school with her school uniform, but later when Chikage accuses her for not being true to herself, Miu discards her glasses and let her hair, including her bangs, to flow freely. When at home, she is usually seen in a purple-spandex outift and other various articles of clothing (including a yellow apron) or a sweater over her outfit, though the spandex outfit is almost always destroyed during any fight she is in. It can be said that she doesn't wear any underwear at home. Although Miu owns and wears underwear and lingerie to school, she notoriously takes it off at home wearing solely her spandex suit. She also constantly wears two red hair-clips, one that flips to reveal a small blade and the other a lockpick, which were gifts from her mother. While not at school wearing her school uniform or her pink gymnastics outfit for gymnastics class, for casual wear, she tipically wears dresses or simple tops or blouses with skirts (despite her stating she doesn't really like skirts due to how they get in the way of fighting).
When brainwashed into Bulu, her hair becomes rather unruly and her eyes are emotionless. During this time, she wears a light blue, one-piece Tidat outfit, without any undergarments along with a light hat and leg guards, while the feet are left bare. The outfit is completed by a bird mask with a long beak and feathers on top to conceal her face.
Despite her arduous past and her numerous chores, Miu has constantly shown herself to be a very kind-hearted, cheerful, gentle, polite and upbeat individual, constantly caring for other people and helping in their needs. Unfortunately in contrast to her gentle nature, Miu’s intense training from her grandfather has conditioned her to by instinct throw people who sneak up behind her; a trait that her grandfather claims to be unintentional on her part, which is something of a running gag of the series.
She is arguably the only one who worries about Ryōzanpaku's financial situation. She can become quite fierce when monetary issues are brought up (so much so that her own grandfather was afraid of the idea of her finding out he spent 100,000 yen). When her fears are finally realized and Ryōzanpaku becomes bankrupt, she becomes determined to push the masters to teach little children in an attempt to gain some income, even intimidating Sakaki into helping despite his protest he doesn't teach kids. Miu's worries about finances can, at times, come across as being greedy; shamelessly asking Kenichi to sell the gold medals he received from defeating YOMI members, being flabbergasted at Akisame's refusal to sell a statue he carved for a high sum of money and immediately deciding to pilfer Rimi's pure gold shoes after defeating her, considering them the "spoils of war" (which Thor notes is the same reasoning as that of a thief).
Also, despite her many positive traits, she has low self-esteem when it comes to social interaction. Growing up with never making any friends, due to her constant traveling and training with her grandfather, Miu initially felt nervous in meeting people. In her previous school, all the other girls were jealous of her high grades, athletic ability, and especially her looks. It is because of this that Miu attempted to moderate her appearance by fashioning her hair into a plain-looking braid and began to wear glasses. Though she eventually discarded them after attempting to convince Chikage to be true to herself only for Chikage to accuse Miu of not being true to herself as well, as Miu now appears without her plain-looking self to her beautiful true self. After meeting Kenichi however, she manages to make quite a few friends over the course of the series due to her kind nature and some help from Kenichi.
Despite being very intelligent in in school and martial arts, Miu has shown a bit of a niave and thoughtless side, such as in certain situations, she notices minor things despite how serious the situation is. Such as when she and Kenichi were on Diego Carlo's ship and there was a bomb, Miu just noted how pretty the view from the ship. Possibly due to her grandfathers continuous training since she was little, her constant travels and life-threatening situations keeping her from doing normal things a child would do, Miu has a very childlike personality when it comes to events that she's always wanted to do. Thor has noted she gave up a lot for the sake of martial arts and missing out on several fun activities, as one of them she's always wanted to do is ride a merry-go-round. Her childishness is shown when she went to the aquarium for the first time, she completely forgot she was supposed to look for Kenichi and instead focused on all the fish and acted very excited and childish. This is also shown in regards to romance, as she noticed how Ukita, Kisara and Freya were in a "love Triangle" as she puts it and acts very energetic in regards to romance or people in a relationship. However, she herself is very flustered and shy when it comes to her romance life and her feelings for Kenichi.
Like Kisara, Miu loves cats such as playing with Renka's hair as it makes her look like a cat and wears the badge of a cat that Kenichi gave her when they were little. She constantly plays with cats any chance she can get and acts in a very silly and lovable manner towards any kind of cats or people with cat like feature, which tends to be a running gag of the series, especially with Renka's hair. Her love for cat goes overbroad went she is feeling lonely (because Kenichi isn't there).
Despite her kind and friendly nature towards others, when angered, Miu is surprisingly terrifying, which is usually caused from her Dou Ki fighting style. Such as whenever her friends are hurt, Miu enters a berserker mode and can't seem to control herself, such as when Sho hurt her friends or when Jenazad tricked Hongo into almost killing Kenichi, Miu loses control of her emotions and attacks in blind rage. Words don't seem to reach her and only by incapacitating her or, as shown with Kenichi, groping her breasts seem to help her regain her senses. Junazard used this to his advantage to brainwash her to make her his new disciple by turning her into a mindless killing machine he calls Bulu. However, when Kenichi brought her back to her senses through his willpower and determination, she was able to break out of Junazard's spell and finally return to normal. Kenichi refers this side of her as "her other personality" that comes out when she loses control of herself. Kenichi noted Miu fears this side of her and tries to supress it due to her fear of hurting someone.
Miu truly treasures the friendships she has made, especially with Kenichi greatly, but seems oblivious to his true feelings for her. She has however, repeatedly hinted towards deeper feelings for him, such as getting embarrassed and flustered when they are called a couple, not being able to understand the relief she feels when Kenichi refuses to go to China with Renka and perhaps most famously, becoming jealous and rather possessive of him whenever another girl shows affection for him. She was also very happy and blushed when she heard Kenichi talk about how much he cares for her. After Kenichi saves her life on the school ski trip, she becomes much more open and physically receptive with him, going as far as to tearfully hug and thank him for saving her and staying alive. Every time Kenichi is left severly injured or returns even safely from a dangerous mission, she's always hugging him admitting how glad she is that he's alright. By the time of Miu being left alone with Kenichi for a while when the masters were missing, in addition to starting to realize Kenichi feelings for her, she appears to have started realizing her own feelings for him, going as far as kissing him on the cheek. While they didn't get to discuss the matter any further, several people at school have since noticed Miu being more cheerful and energetic, as well as as more eager to be around Kenichi. As stated by Junazard's observations of her around him even under his control, Miu's feelings for Kenichi have developed even further and has fallen in love with Kenichi (though Miu doesn't seem to be aware since she was brainwashed at the time). Miu has even stated she does not mind dying for Kenichi so he can live and placed his hand on her heart stating she has the utmost faith in his ability to protect her.
While still an infant, Miu's mother died in battle. To save her, Miu's mother buried her lightly under snow with an air-hole. Fortunately, she was found in time by Hayato and had since then been in her grandfather's care. It was in these early years of her life that Miu learned martial arts from her grandfather which she showed a prodigious talent for and also accompanied him on his missions to bring about peace.
Apparently, when a six-year-old Miu and her grandfather passed through Kenichi's old neighborhood, she inspired Ryūto and Kenichi to become stronger after they witness her beat three thugs. Shortly before the fight, Kenichi exchanges her Yin Yang badge with his cat badge, something that she still treasures to this day. Though Kenichi initially did not remember their first meeting, Miu had suspected who he was from their first encounter in the series. When she first met Sho, he had her come with him to know more about her father but was stopped by Kenichi. The Elder said that Miu had a trauma that seems to involve the winter and her parents. At some point she was lost a sea waiting of her grandfather to find her.
Before Miu transferred to Kouryou High School she attended a school that was apparently quite famous but didn't fit in because all the girls in the school were jealous of her high grades, athletic ability, and especially her looks. It is because of this that Miu attempted to moderate her appearance by fashioning her hair into a plain-looking braid and began to wear glasses.
Despite Miu's gentle nature, she has consistently proven herself to be a very strong and talented fighter. Odin once described the way she fights as "being like a feather that can slice through the wind". Kenichi has never once been able to hit her in a sparring match (though his vow to never hit women much less Miu may contribute to this, as well as his unwillingness to fight unless to protect others). She has also said that she could only spar seriously with Kenichi recently, meaning she had always been taking it easy on him in the past. Even more so, Silkwat Junazard, a master of Yami known for having exceedingly high standards for accepting students, was greatly eager to make Miu his disciple. Since her training under Junazard, Kensei has noted that her skills have increased greatly to the point that even when she tries to hold back, she can take out most people with little effort.
- Innate Talent: Miu has repeatedly shown to be highly capable in a large variety of areas; far more than one would expect of a teenager still in high school. Since young childhood, Miu has been able to quickly learn and improve at seemingly anything she puts her mind to. Even then, she was able to fight off several full-grown men with relative ease. Furthermore, in just one week, she perfectly mastered the basics of Pencak Silat and several of its techniques, becoming able to easily defeat multiple highly skilled fighters purely with Pencak Silat. In addition to her natural aptitude for martial arts, she also excels in all forms of sports and has also taught herself a number of household skills to help make her home better maintained.
- Keen Intellect: Miu has regularly shown intelligence and instincts much keener than her looks and demeanor would suggest. Even with the constant training she undergoes and chores at home, Miu has maintained a perfect academic score. Outside of basic school studies, Miu has shown highly honed battle instincts and cunning from experiencing countless fights and extensive training by her grandfather since early childhood. Miu is able to quickly comprehend the situation of a battle to quickly decide on the proper method to handle it. Having trained and learned extensively from her grandfather, Miu has accumulated an extensive and detailed understanding of combat in its various forms. She is also highly perceptive; simply from observing her opponent's bodystance or physical-build, she can deduce the nature of her opponent's fighting style.
- Great Physical Prowess: Miu's constant training has pushed her body to the peak of physical condition, well beyond what her feminine build would suggest. She is a highly accomplished gymnast and acrobat, making her the ace of her gymnastics club since day one and which she uses to her advantage in battle. She possesses seemingly inhuman flexibility and dexterity, able to contort herself to effortlessly maneuver through most terrains. Her agility and balance also border on impossible. Repeatedly, she is shown able to nimbly scale any obstacle, jump across town from rooftop to rooftop, never losing control, and being able to effortlessly shift her body position even in mid-air.
- Enhanced Strength: While certainly not the most intimidating in appearance, Miu has also shown deceptive raw strength, able to easily break apart a punching pole rooting in the ground and send it soaring. In battle, Miu is seen regularly holding back a considerable amount of strength, as she wishes to avoid injuring her much weaker opponents as much as possible. Her strength from Junazard's training has grown to the point that now she can cause heavy injuries even when she tries to hold back.
- Immense Speed: One of Miu's most noticeable battle traits is her speed, able to react against incoming threats at a moments notice, dodge unscathed, disarm her opponents without their noticing, and manuever as if disappearing from unfocused eyes. Even against Master Class fighters, Miu is able to follow their movements to just avoid damage. Her attacks are shown to be swift and accurate, able to take down weaker opponents in an instant. After her training from Junazard, her speed is great enough to now easily surpass Rimi's speed at her best while still considerably holding back, despite the latter claiming she's gotten much stronger since last time.
- Immense Dou Ki: Despite her young age, Miu has been noted to have a very high level of Dou Ki and is capable of having a powerful aura around her when she lets her emotions get the better of her. Such as when Sho tried to kill her friends, she lost control of herself and her Dou Ki caused her to enter a Berserker Mode, attacking everyone around her allies or enemies and is unable to control herself unless someone is able to calm her down. The Elder claims because of her high Dou Ki, she is capable of inflicting great pain to those around her should she lose control of herself. Since her training under Junazard, any small fluctuation on her emotions causes her to lose control and she can cause heavy injuries even when trying to hold back. After her training with Kensei and Akisame, Miu now finally has gained some control over her Ki and can use it effectively in battle without it controlling her. However, should she use it for too long and lose control of her emotions again, her Ki would take control of her again. Kenichi states when she loses control, she becomes the "other personality" Junazard made when training her. Once Kenichi told her not to be afraid of her Ki and he'd be there for her, Miu seems to have finally mastered her Ki, having no longer has a berserker like look in her eyes when fighting and seems to be in control.
- Enhanced Endurance: Despite her slender and womanly frame, Miu has constantly shown to have a strong amount of stamina. Such instances have been shown when she was kicked in the side by Boris Ivanov multiple times and only sustained a minor rib fracture and even an kick from Christopher Eclair only sent her backwards. Even after having taken numerous blows from Rimi in their third fight, several of which caused Miu to lose blood and possibly break some bones, Miu was still able to fight with coniderable strength. After taking even further damage from Rimi while she was using Seidou Goui, Miu was able to stay conscious and even attempt to attack Ogata and even managed to survive a strike from S-class master, though the damage knocked her out.
- Hybrid Martial Artist: Miu's training in martial arts does not seem to focus on any single discipline, nor is her style completely known, outside of it being her family's developed style. While her fighting style is mostly fluid with aerial and kicking-based attacks, Miu has shown proficiency in jabs, takedowns, throws, body-locks, counterstrikes, and so on. Miu has also used her skills in gymnastics as a focus point in her style, often using the flexability she has gained from gymnastics to perform movements and contort into positions that not only makes her a difficult opponent to catch, but allows her to attack in ways that take advantage of her flexability and unique fighting style at the same time. Her style of combat also is more unorthodox, regularly able to adapt to any situation and use any item or part of the battlefield to her advantage. After her training with Junazard, she learned how adapt the basics of Pencak Silat to her repertoire, making her an even more versatile and dangereous fighter.
- Expert Spy: Having assisted her grandfather on missons for years, Miu has developed considerable skill in espionage. She can skillfully enter any stronghold undetected, pick locks, hide necessary accessories of person, and disarm bombs.
- Killing Intent: Thanks to The Demon God Fist training her Killing Intent has become even stronger than most people to the point now that she will kill someone if she loses control for her emotions and enter her berserker mode.
- Anatomy Control: Not unlike her grandfather, Miu is able to regulate the energy flow in her body. She is able to transfer energy at will, from her speed into her strength and vice-versa. Also she is able to suppress her energy entirely to hide her presence from others.
- Master Homemaker: While only a teenager, Miu excels in all areas of housekeeping. From sewing and laundry, to cooking and cleaning, Miu has shown expert skill in each of them. She has become somewhat infamous for her culinary skills, able to prepare any kind of meal with great presentation and highly edible.
- In a good portion of her fights, Miu's cloths get ripped in some way by Master (or Disciple) Class Fighters.
- Miu bears a heavy resemblance to Street Fighter character Cammy White and shares quite a number of traits with her: both have blonde braided hair with a bang sticking from the top, blue eyes, a fondness for cats and similar looking fighting styles.
- During chapter 316, Miu decided to be honest to herself. She stopped wearing fake glasses when in school and also she doesn't braid her hair anymore.
- Miu is one of four girls that has fallen in love with Kenichi. The other three are Renka Ma, Raichi Li and Yūka Izumi.
- Miu's dream is to become a beautiful bride. Ironically, her dream of becoming a beautiful bride is made extremely difficult by her grandfather's unreasonable declaration that Kenichi must defeat him in order to be with Miu. This is made more ironic due to the Elder only being concerned for Miu. Ultimately however, after the series' conclusion, Miu finally achieved her dream, marrying Kenichi.
- She, along with Kisara Nanjō, is fond of cats.
- She is bad at lying.
- Her name is written with the characters for beautiful (美) and feather (羽). The name Jenazad gave her is an exact translation of her Japanese name, since "indah" means beautiful and "bulu" means feather in Indonesian.