[Iron Sugar] Gal na Imouto no Umi Ryokou ni Doukou Shitara Doutei Soushitsu Suru Koto ni Natta Hanashi [Full Color] [ChoriScans]

A trip to the sea with his gyaru little sister and her cute friend Miu takes a turn when the shy virgin big brother gets an eyeful of the girls' new bikinis—and his teasing sibling decides her flustered onii-chan needs hands-on relief. What begins as playful nipple teasing under the beach umbrella escalates into a secret outdoor pounding right under her friend's nose, complete with a reckless creampie that leaves her scolding him about safe days and babies. Sibling banter, gyaru attitude, and a sister who loves pushing her big brother's buttons make this a steamy summertime taboo fantasy.