"It's a Family Affair" centers on the intricate dynamics of the Takahashi family, whose lives are upended when long-buried secrets and unresolved tensions resurface. The patriarch, Hiroshi Takahashi, is a stoic businessman whose rigid demeanor masks a troubled past. His wife, Akiko, struggles to maintain harmony within the household while grappling with her own unspoken regrets. Their three children—eldest son Kenji, middle daughter Yumi, and youngest son Taro—each navigate their unique challenges, reflecting the generational divide and societal pressures in contemporary Japan.

The narrative unfolds as Kenji, a disillusioned salaryman, returns home after a failed business venture, forcing him to confront his strained relationship with Hiroshi. Yumi, a college student, becomes entangled in a romantic relationship that challenges her family's traditional values, while Taro, a high school student, faces bullying and identity struggles. The family's fragile equilibrium is further disrupted when a mysterious letter arrives, revealing a hidden connection to a long-lost relative. This revelation sets off a chain of events that forces the Takahashis to confront their past, reconcile their differences, and redefine their understanding of family.

Themes of forgiveness, resilience, and the complexities of familial bonds are explored as the characters navigate their individual arcs. Hiroshi's gradual softening and Akiko's quiet strength provide a counterbalance to the younger generation's struggles, creating a nuanced portrayal of intergenerational conflict and growth. The series balances emotional depth with moments of levity, offering a realistic yet hopeful depiction of a family's journey toward healing and unity.