Nanashi is a teenage boy with messy, medium length dark hair, with a single bang that covers his forehead, and also has freckles on his face. After meeting a Samurai, he begins wearing his hair in topknot to emulate his idols. He wears a light colored shirt with the kanji for "seven" (
Nanashi is a kind and optimistic boy, and brave young boy. Like his sister, he has a stutter, one that is exacerbated when he is afraid. Unlike Ann, he is much more outgoing and energetic. Nanashi is fascinated with Samurai, to the point where he mimics the fashion styles of Samurai. Despite being a Nanashi, he wishes to avoid a life obscurity. Nanashi is also ambitious, stating his desire to become the galaxy's Grand Stellar Shogun. Thanks to this love of Samurai and his desire to stand out, he made it his goal to become the most powerful and famous Samurai in the galaxy with Ann serving as his Princess.
Despite his dreams, Nanashi's primary goal in life is to care for and protect his adoptive sister. Despite having little, he does all he can to look out for Ann. He will also defend her from anyone, even when he is afraid. Ann's safety is paramount to him, and anything perceived as a failure to protect her is emotionally devastating to him. He is willing to run any risk if it means being able to protect Ann or becoming better at doing so. This is evidenced by his willingness to commit seppuku to become a Samurai before receiving the training to earn the right to even make the attempt.
Nanashi, after making a promise to Ann's mother to look out for her, cared for Ann to the best of his ability. Along the way, he changed her name from Nanashi, the title given to orphans, to Ann. Nanashi often protected Ann from bullies, only to wind up getting beaten thanks to the difference in skill and number. Despite the losses, he resolves to protect his sister.
One night, Nanashi explained that he had seven dreams for the future, all of which center around becoming the greatest Samurai in the galaxy with Ann as his Princess, at which point he changed the spelling of his name from the kanji for "nameless" to those for the phrase "seven desires" as a reflection of his goals. Though he winds up listing off eight dreams instead of seven, he keeps the last one because it was the most important to him: protect Ann as long as he lives. Nanashi also has an encounter with Hagamichi and Un after getting to close to a Locker Ball on display.
When Nanashi gets into a fight with bullies again, Ann is knocked out when she rushes to defend him. Her actions scare the bullies off, but Nanashi is devastated that Ann was hurt on his watch. Driven to be a better protector Ann, he goes to the Locker Ball in Akagi Castle and commits seppuku with the blade associated with it. Though he tells Ann, who he brought along, that he would become a Samurai capable of protecting her, the Ball does not respond to him, and he dies before her eyes.
- Nanashi's name was initially spelled out using the kanji for Nameless (
名 無Nanashi?), a generic name given to orphans on his world. He later rephrased it to means Seven Desires ( 七 志Nanashi?).