Ryoko Izumo is a determined, tough and healthy high school girl from Japan who looks for the meaning of fighting to become a true fighter. She is also is a disciplined and diligent Japanese judo practitioner and sports superstar who fills the hearts of the people in her hometown with pride. When a young Ryoko was training with her father Goro Izumo, she threw him so far away he actually became lost. She hasn't seen him since then, and therefore has been raised andd trained by her grandfather Sanshiro Izumo and her seniors Love and Aya for years. Ryoko is so focused in battle that her body learned to instinctively react with violence when coming with physical contact with someone else. She also has problems maintaining both Judo and her studies, often arriving late to class due to competitions. Even though she is a student, Ryoko has troubles with basic Math and English.
However, Ryoko journeys the world picking fights with other warriors, until one day she is invited by her opponent in a street fight to a tournament named "World Heroes", which will be held once again. The opponent in question was the Iga Ninja Hanzo Hattori. Admiring Hanzou's strength, Ryoko accepts to take part in it. She is also comes to know Jeanne D'Arc, whom she respects for being strong and beautiful and wishes to surpass one day, like an older sister, even though Janne only sees her as a kid. At the end of the tournament, she returns to Japan. Shura Nai Khanomtom also has an unrequited love towards Ryoko, even though she recognizes hes talented
Ryoko went around challenging inumerous dojos to test herself even further. She ends up being a Judo hustler, winning against many Judo fighters around the country. When a new World Heroes is held, she participates encouraged by the idea of meeting Hanzou again. Ryoko ends up developing a crush on Hanzo, visits him often and even goes out with him once, but he remains unaware of her feelings and only sees her like a sister.
Dr. Sugar Brown agrees to let her use his time machine to travel to different eras seeking new challengers in tournaments. In one of these travels, she ends up meeting the fighter Lee Hae Gwon, who teaches her one of his moves, and Kisarah Westfield, a friend of Dr. Brown whom tells Ryoko that the ninja Fuuma Kotaro ended up being lost in that time not long ago. Dr. Sugar Brown, the organizer of the World Heroes tournament, has located Ryoko's father Goro for her. As well as they rush each other for a hug, Ryoko unconsciously throws her father so far away to the point he gets lost once again in the world. In tears, Ryoko screams for him without success, while Brown remains surprised at what happened.
Ryoko is an easy-going girl and very kind. Also, due her training she's accustomed to do complex techniques, like throwing, but sometimes wants to carry a normal life like any teenager. It's implied to be in love with Hanzo.