My big brother brought his girlfriend home. Her name is Aika, a cute girl with big breasts. Shota-kun catches them making out in the room, and overwhelmed by jealousy and mischief, he thinks, "She's too good for my big brother! I want to touch her boobs too!" During a game of cards, he takes full advantage of punishment dares—giving her handjob and teasing her with a toy under the table. They take a bath together, and he shamelessly gropes her large, soapy breasts, exploiting his status as a child. Then he sneaks into their room late at night after spiking their drinks with a prank, creeping in while they're asleep...