Mai Otonashi, younger sister to Ginya, shares a childhood marked by abandonment and loss. Their father, Kojirou Shinbashi, deserted the family early in their lives, leaving them in the care of an aunt and uncle who bestowed the Otonashi surname. The siblings’ mother, Sakura, died during their youth, with Kojirou conspicuously absent in her final hours—a void that etched enduring fractures in the family’s emotional foundation.

Mai’s history intertwines with Ginya’s pursuit to unravel their father’s legacy, including his role in designing the Yozakura #1 pachislo machine, a linchpin in the unfolding story. Though the narrative does not elaborate on Mai’s active participation in these events, her existence anchors Ginya’s resolve to reconcile Kojirou’s abandonment and its lingering repercussions on their fractured family.