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)…!?

It is a sequel to the commercial work "Big Sister-in-law, Attack", but this is the only thing you can read. Alice, a sister-in-law who came from Scandinavia due to her parents' remarriage. Since I couldn't stand her big breasts and got her hands on them, they have continued to have a forbidden relationship. One summer day, I decided to go to the pool for special training for Alice, who couldn't swim. Of course, I couldn't suppress my reason with the big breasts overflowing from my competitive swimsuit, so I secretly had sex in the shower room. Of course, that doesn't stop there, and I get pregnant and have sex at the hotel. Sex with my blonde big sister-in-law.