Saikin, Imouto no Yousu ga Chotto Okashiinda ga Temporada 1 Episódio 12

Mitsukis his little sister, and Yukina is an older sister figure. To Yuuya, both of them are precious family members. But on one morning of their stay at the hot-springs, Neko hypnotizes Yuuya to be more honest, and he calls Mitsuki really cute and gropes Yukinas breasts.