Yasuo Yasuda, nicknamed Razor Blade Yasu, entered Suzuran High School as a small-statured freshman lacking fighting skills, making him a frequent target for bullies. His path crossed with Harumichi Bouya during harassment by Akutsu Futoshi and his gang; Yasuda persuaded Bouya to step in by showing a picture of his sister. This encounter forged an immediate bond, establishing Yasuda as Bouya's first underling and closest friend, despite Bouya's initial resistance to forming ties. Bouya quickly came to rely on Yasuda for crucial information about Suzuran.

Within the informal Harumichi Family, Yasuda evolved into the unofficial "number two man" or vice-head, though Bouya consistently viewed all members as friends rather than subordinates. The group swelled to around fifty members during intense conflicts like the T.F.O.A. war. Yasuda's loyalty to Bouya proved absolute, enduring even after adversaries kidnapped him to lure Bouya into a trap. This harrowing experience unexpectedly led Yasuda to form friendships with fellow unlucky students Susumu Sagawa and Tamasu Tsuyoshi.

Progressing through sophomore and senior years, Yasuda transformed from a simple follower into one of Bouya's most trusted confidants. His non-combative nature remained, yet his unwavering dedication solidified his position. After graduation, Yasuda struggled to find employment, hampered by Suzuran's notorious reputation. Juniors occasionally sought him out years later, hoping for information about Bouya’s whereabouts, highlighting his enduring link to the family's legacy.

A middle school aspiration to become an actor was noted for Yasuda. His entire Suzuran journey underscored his reliance on fierce loyalty over physical prowess, cementing his role as a pivotal yet unconventional figure within the group's dynamic.