Chitose Hitotose, an orphaned high school student, lives alone in his family’s home after his parents perished in a marine accident. Initially withdrawn and indifferent, his solitary existence shifts when five teachers move in as surrogate mothers, determined to bolster his academic performance and emotional well-being. His surname, meaning "compassionate age," echoes the narrative’s focus on empathy and personal growth.

Following the maritime disaster that claimed his family, he resided in an orphanage, forging sibling-like bonds with Minazuki and Hazuki, who later become his adopted sisters. Minazuki nurtures a childhood crush, while Hazuki assumes a protective role. His early delinquency—marked by physical confrontations with peers who taunted his orphaned status—reveals a defensive exterior concealing vulnerability.

Guided by his teacher-mothers, Chitose undergoes profound growth. Mutsuki Ichimonji, his homeroom teacher, becomes pivotal as their relationship evolves from mentorship to mutual romantic affection, culminating in a kiss by the final season. Eccentric Kisaragi Ninomai challenges him with scientific experiments, while Satsuki Gokajo balances aggressive caregiving against Yayoi Sanzenin’s spiritual guidance and Uzuki Shitenno’s playful antics.

His rivalry with Nagatsuki Kuron, rooted in competing for Mutsuki’s attention and shared combat prowess, evolves into mutual respect, leading her to join his familial circle. Classmate Fumitsuki Nanakorobi further complicates his social world through persistent, unrequited affection.

Chitose’s journey from isolation to emotional openness unfolds amid reconciling past traumas, defending loved ones during crises, and navigating romantic tensions. The narrative concludes with his teacher-mothers symbolically transitioning into marital roles, mirroring his maturation and acceptance of their collective impact on his life.