Matsuri Toba, the 18-year-old cousin of the four Ryudo brothers, lives with them and infuses their home with a nurturing presence. She manages household duties like cooking and cleaning, serving as a steadying force against the brothers’ chaotic lives. Her relationships with each sibling reveal layered dynamics: playful banter with Tsuzuku, a protective maternal role toward the youngest brothers Owaru and Amaru, and a respectful yet tension-laced dynamic with the eldest, Hajime. Subtle undercurrents imply unspoken feelings for Hajime, though their bond remains firmly familial.

Her family history is shaped by friction with her father, Seichiro Toba—the ambitious head of Kyowa College, who values personal gain over kinship. Matsuri openly resents his manipulative schemes, including efforts to undermine Hajime’s standing at the college. In stark contrast, she cherishes her mother, Saeko Toba, daughter of the Ryudo patriarch, whose quiet dignity commanded the brothers’ respect. Saeko’s union with Seichiro, implied to be rooted in strategy rather than affection, strains Matsuri’s loyalties between blood and chosen family.

Beyond domesticity, Matsuri is drawn into the brothers’ battles against external threats, acting as their moral compass to reinforce unity and mutual protection. The siblings fiercely guard her in return, their bond a pact of unwavering devotion. Though she avoids physical combat, her quiet fortitude and emotional resilience cement her pivotal role in balancing the group’s volatile energy.