After his parent’s remarriage, the protagonist Takashi becomes stepsiblings with Alice, hailing from Scandinavia. Though bewildered by her overly large breasts, he’s tried hard to treat her properly as a brother. However, one day when he accidentally sees Alice naked, the thread of his self-control finally snaps! Takashi then challenges her to a “contest” over which is superior—woman (breasts) or man (cock)…!?