Mako Oda, a voluptuous married woman living in Tokyo, takes in her nephew Ken, a college entrance exam student, to stay at her home. Mako always goes braless, her huge breasts clearly visible through her loose loungewear, her erect nipples constantly distracting Ken and breaking his concentration. Unconsciously, she keeps teasing him with erotic behavior. As Ken's patience nears its breaking point, Mako discovers he's still a virgin. Overcome with desire, she abandons her role as a protective aunt and begins actively seducing him.