Miyu, the stepmother, has a naturally airheaded and carefree personality, constantly being called "clumsy" by her husband every day. Despite this, she surprisingly possesses huge breasts, which her son-in-law Nob finds intensely arousing. Under the pretense of mending the family's relationship, Nob draws closer to Miyu and begins fondling her massive tits. Unaware of Nob's true intentions, Miyu repeatedly reaches orgasm, gradually getting deeply entangled in an affair with her son-in-law—unknowingly abandoning her husband and daughter in the process.