Mitsuki Mashiba, twin sister of Youhei Mashiba, balances her current life as a polished insurance agent clad in sharp red business attire with the lingering shadows of her delinquent past. Once sporting puffy blonde-dyed hair and a yankee schoolgirl uniform under Kyouko Shirafuji’s leadership, she now embraces brown hair and professionalism, though a fist knuckle tucked away hints at her former life—a relic she darkly jokes is an “extra service” for clients.

Her fraught bond with Youhei crackles with rivalry, their interactions laced with barbed critiques. Both twins share an unshakable loyalty to Kyouko, forged when she defeated Youhei, compelling them to join her gang. Mitsuki still answers Kyouko’s summons, aiding at Wagnaria during chaotic shifts, her admiration undimmed.

Fiercely protective of Yachiyo Todoroki, Mitsuki views Jun Satou’s affection for her as a challenge to Yachiyo’s autonomy, fueling her disdain for him. Determined to reinvent herself, she bristles at reminders of her rebellious youth—particularly old photographs Youhei gleefully circulates—yet cannot fully shed her past. Aggressive reflexes surface when provoked, and the knuckle remains a stubborn keepsake.

Kyouko’s influence once molded Mitsuki’s brash demeanor and style, but her shift to a conventional career underscores a tense duality. She champions her reformed identity while wrestling with residual ties to her former self, caught between polished respectability and the pull of old loyalties. Clashes with Jun, volatile exchanges with Youhei, and reluctant cooperation at Wagnaria lay bare her struggle to reconcile who she was with who she strives to become.