Hoping for a fresh start, househusband Masaki Fujiyoshi, his spouse Hiromu, and their toddler son, Hikari, move to a new neighborhood. The couple's union was frowned upon by many due to Masaki's status as an omega—a secondary gender that allows an individual to give birth. Even for an alpha—seen as the superior secondary gender—such as Hiromu, discrimination seems to be commonplace and a hindrance to a life of domestic bliss.

Fortunately, the new family is not alone. Little Hikari becomes attached to Yuuki Hirai, the Fujiyoshis' lonely college student neighbor. Despite his initial reluctance, Yuuki ends up befriending the infant. Moreover, the family can also confide in Hiromu's childhood friend and coworker Tomohiro "Matsu" Matsuo.

Although everything is going well for the young couple and their child, a sudden presence from the past might pose a problem for the peaceful life they dream of.