Masa is a former yakuza underling from the organization previously headed by Tatsu. He often unwillingly aids Tatsu with domestic duties and errands, even after Tatsu's retirement from yakuza life.

Initially, Masa balks at Tatsu's shift to domesticity, finding it hard to square his ex-boss's formidable past with his current role as a househusband. Gradually, however, Masa perceives unexpected similarities between household management and yakuza operations, prompting him to reassess these domestic responsibilities.

His interactions span beyond Tatsu, involving encounters with other ex-yakuza adapting to civilian life, such as Torajiro—an ex-rival gang leader now running a crêpe truck. Masa actively engages in various domestic situations alongside Tatsu, including navigating discount stores on shopping trips, attending New Year celebrations, and mastering household budgeting intricacies.

These experiences steadily reshape Masa's understanding and acceptance of Tatsu's path, though he retains his earnest nature and frequent bewilderment throughout the adjustment. His development reflects an ongoing adaptation to the mundane demands of civilian life, still colored by ingrained behaviors from his yakuza past.