Ane no Seiyoku Shori wa Otouto ga Suru Mono da to, Gitei wa Omoi Hajimeteiru.

The big sister who's always taking care of her stepbrother's sexual relief has apparently started to like being done "harder" lately... This time, her request is to be fucked harder than usual. He grabs her by her charm point: her ponytail, and does his best at being a bit rougher with her boobs and a little more forceful during blowjobs. The little brother has begun to think that taking care of his stepsister's sexual urges is his responsibility. (Source: DLsite, translated) Released at Comiket 100.