Eldest son Hideki is responsible and mature, while younger son Kenji is a clingy mama's boy. Both were born from Eiko's childbirth-ready hips, yet their personalities are complete opposites. Kenji openly clings to Eiko's ass without caring what others think, while Hideki, as the eldest, suppresses his own desire to seek affection and fulfills his duties instead. One day, Kenji accidentally catches Eiko in the middle of her daily dildo masturbation routine. Seeing his mother's big ass up close, Kenji's gaze gradually turns passionate. Unable to contain his growing desire for her voluptuous rear, he begins expressing his affection as her younger son in an entirely new, intimate way.