Michiru Sanjou, a talented volleyball player who earned selection to Japan's national team, the Best Twelve, initially greets protagonist Kozue Ayuhara with hostility. This antagonism springs from unresolved personal trauma tied to a tragic family incident. Her older brother, her only family member and deeply invested in volleyball, disappeared after an accident during his university club activities. This loss made Michiru associate volleyball with pain. In a moment of anguish, she destroyed the volleyball he gave her, stabbing it in a frenzy, though she kept the deflated ball as a sole memento. This event fueled her deep resentment towards the sport and those who pursued it passionately, especially Kozue, creating competitive friction within the team.

Michiru's icy demeanor gradually thaws as she confronts her past and processes her grief. This internal journey leads to reconciliation with Kozue, shifting their relationship from antagonism to mutual respect and cooperation. Her character arc charts a path from bitterness toward acceptance and teamwork. Beyond rivalry, Michiru's story underscores themes of trauma and recovery within competitive sports. Her integration into the team signifies overcoming personal demons and embracing collective goals alongside former adversaries.