Rantaro Amami is a student in Ultimate Academy for Gifted Juveniles and a participant of the Killing School Semester featured in Danganronpa V3: Killing Harmony.
Rantaro's talent is unknown at the start of the game. He claims that he does not remember his talent and is not particularly concerned about discovering his talent. Thus, he is dubbed Ultimate ??? (Super High School Level ???).
After he successfully joined Danganronpa as a Killing Game participant, Rantaro's memories and past were fabricated by Team Danganronpa as follows. Rantaro claimed he came from a very rich family and that he was raised like a celebrity. He had multiple younger sisters, most of them were stepsisters. Many years ago, he and his entire family went on a boating trip. It was Rantaro's first one. He liked traveling and once they reached a port, he got off the ship and went on an adventure. His youngest sister followed him off the boat without him realizing and as a result, she disappeared and was never found. Rantaro blamed himself for her disappearance, believing himself to be a terrible older brother and feared that his sisters might hate him.
However, Rantaro was determined to find his sister and with his father's permission, he traveled around the world on a boat searching for her, while simultaneously helping with his father's business in search of new markets. He believed that his sister was alive unless he was proven otherwise. The traveling was dangerous, especially when he had to cross territories. He gained his Ultimate Adventurer title during one of his journeys through the savanna when he came across a remote village and helped the villager with their research about a rare disease that only affected the people there. He began to get famous after that, traveling the world, and eventually, people were calling him the Ultimate Adventurer. Somehow, Rantaro lost all of his 12 sisters all around the world, and his family and everyone else told him to give up. He is determined to reunite his siblings no matter how many years it would take him.
While never actually seen, slight aspects of Danganronpa 52 were made clear during the Killing School Semester. Rantaro was one of its participants and had the title of Ultimate Adventurer. In this Killing Game season, Rantaro was one of the participants who survived until the very end. He and supposedly one other person chose to sacrifice themselves in order to let hope win, which would lead to him being punished. Rantaro was completely unaware that the form of punishment was not to have his life taken but to participate in the next Killing Game. As a result, his memories of Danganronpa 52 were erased and he was given the title of Ultimate Survivor (超高校級の「生存者」 chō kōkō kyū no “Seizon-sha” lit. Super High School Level Survivor), replacing his original talent as the Ultimate Adventurer (超高校級の「冒険家」 chō kōkō kyū no “Bōken-ka” lit. Super High School Level Adventurer). He was also given special "perks" for surviving that he could make use of however he wanted in the next Killing Game.
Rantaro is relatively good-looking and it is noted in the game that he looks like a "playboy." He has curly green hair and two small ahoges sprouting from the top of his head. His eyes are green and have notably long, thick eyelashes. He wears a dark blue striped sweater that has a chain accessory pinned to it, with baggy, light-brown sarouel pants, and slip-on shoes. His sweater has a big dark symbol resembling his former high school, Hope's Pass High School, as well as a symbol resembling a boats steering wheel, and the setting sun. Rantaro wears a necklace with a crystal pendulum hanging at the end of it. He also wears a silver bracelet on his right wrist and a different, larger bracelet that wraps around his left wrist several times. He has multiple silver rings: one on his left index finger, one on his right thumb, and one on the right index finger. His right middle finger has a one bigger and darker ring. His right ear has six piercings, one being a beaded earring unlike the rest, while his left ear only has one bead earring. His official design sketches show him with a one silver piercing on his right eyebrow. However, this is not included in the game. In the prologue, he wears the uniform of his original high school. He wears indigo-colored pants with brown cardigan and loafers. His clothes look rowdy, letting the tri-colored necktie loose and having the sleeves rolled up.
When he was first introduced, Rantaro seemed like a mysterious individual. Later it could be seen that he is a carefree and relaxed person, and he is actually described as one of the more ordinary students despite his mysteriousness, with he himself stating that he can sometimes get a bit overwhelmed by the others' stranger personalities. Nevertheless, he is shown to have more patience with some eccentric students like Kokichi and Miu Iruma, with a tendency to just laugh off some of the things they say. Even though Rantaro cannot remember his talent, he doesn't seem worried about it, instead, he simply looks forward to finding out what it is. He is usually seen smiling and describes himself as "not a suspicious guy". He gives off a really calm and composed vibe and seems like a reliable person. His speech is characterized by being very friendly and colloquial, using the "～っす/-ssu" copula in his sentence (in the Japanese release only). Fan translations usually adapt this pattern by using teenage slang in his lines.
Despite his appearance and manner of speech, he has cold, excellent insight, and he is both determined and brave. He even has downright frightening expressions whenever he gets very serious. While the other students descend into confusion and chaos when Monokuma and the Monokuma Kubs state their objective, he is capable of coldly interrogating them about their motives. He also shows a deep understanding of the situation and often talks and acts like he knows something the others don't know, saying profound-sounding and enigmatic sentences, which often make him sound quite suspicious or even eerie. He is shown to be very competent in the Killing Game scenario, understanding that in order to truly win the game you must end the game itself instead of outwitting other participants, and he warns Kaede about her inspirational speeches and strong cooperation with others because it makes her a notable threat in the eyes of the mastermind. During his Free Time Events with Kaede, she notices that he calmly observes other students and makes logical assumptions about them. He plans to end the Killing Game, telling the others not to intervene, but he ultimately fails because of Kaede's actions.
People (especially girls) occasionally seem to assume that Rantaro is a womanizer, he himself is aware that he looks like a "playboy", but he always insists he isn't that kind of person and he doesn't have a girlfriend, stating that he's just a chill, friendly guy. Apparently, he dislikes it when people assume that he is a womanizer or the kind of person to quickly hook up with someone based on his looks, possibly because his father might be one. During the cutscene with him, Kaede and Tsumugi in Chapter 1, the two girls talk about how his looks give the impression of a playboy while he really isn't that kind of person at all, though in the English version Tsumugi also seems to assume that he might be gay considering his insistence on not having a girlfriend and his somewhat stereotypical mannerisms.