Manabu Yasui is a professional 6-dan shogi player. He copes with shogi losses by consuming alcohol excessively, often leading to violent drunkenness, a tendency known among other players. Kyoko Kouda specifically warns Rei Kiriyama about Yasui's behavior before their scheduled match.

Yasui's impending divorce is scheduled for after Christmas. His critical shogi match against Rei Kiriyama occurs on December 24th. Victory in this match would allow Yasui to spend Christmas with his family before the divorce, while a loss would likely trigger his destructive drinking habit and prevent this final family gathering.

Yasui shows a reluctance to analyze his losses or adapt his strategies, choosing to drown his failures in alcohol rather than engage in constructive self-improvement. This avoidance extends to his personal life; he initially neglects Christmas presents intended for his daughter, choosing to drink instead of fulfilling his familial role during their remaining time together. Rei Kiriyama observes this behavior, noting Yasui's repeated failure to learn from either his shogi defeats or his collapsing family life.

Yasui serves as a narrative counterpoint, illustrating a potential path of stagnation and self-destruction that contrasts with Rei's journey. His character arc provides a study in the consequences of 逃避现实 and the cyclical nature of unresolved trauma within professional shogi.