Yōhei Mashiba is a 26-year-old man with grey hair pulled into a ponytail, sienna brown eyes, and a noticeable snaggletooth. His typical attire includes a green jumpsuit layered over a white t-shirt, paired with brown shoes. Originally part of Kyouko Shirafuji's disbanded gang, Mashiba retains fierce loyalty to her. This devotion prompts his temporary stint at the family restaurant Wagnaria during staffing crises, though he deliberately avoids permanent employment to remain on-call for Kyouko's needs. His personality bursts with hyperactive zeal for tasks assigned by Kyouko, yet he falters at fundamental duties like memorizing orders. He openly admires Wagnaria's staff, considering them exceptionally competent due to their link to the "Boss" (Kyouko), and mirrors this energy in his rapid-fire speech. Mashiba shares a contentious dynamic with his fraternal twin sister, Mitsuki Mashiba. He resents her perceived arrogance and disrespect, stressing their contrasting appearances and his seniority as the elder sibling, fueling their persistent antagonism. A subplot reveals Kozue Takanashi developing romantic feelings for Mashiba after he casually compliments her post-breakup. He rebuffs her advances, citing practical concerns over his unemployment and financial instability. This tension gradually shifts, culminating in a physical relationship by the series' end. Throughout official media, Mashiba’s role remains consistent: a recurring support character defined by unwavering loyalty to Kyouko, friction with his sister, and a slowly evolving connection with Kozue.