Garden: Takamine-ke no Nirinka The Animation / Garden: Two Flowers of the Takamine Family

The main character of the story, Tomo-kun, was adopted as a teenager into the family of his distant relatives Takamine, because his parents, for some reasons, had to move abroad. Since then, he has lived with his new family: a damn attractive for her age adoptive mother Kasumi-san, and her two daughters, no less sexy little beauties, the free-spirited weirdo Takamine Ayane, who loves to wear a swimsuit under her clothes, and the serious and strict but very caring Takamine Sayuri.
Time passed, the guy grew up, and hormones made themselves known; he had to put more effort into fighting dirty thoughts, but with such a family it was hardest of all, because the girls behaved too frivolously in the presence of the guy.
Everything started on the day when Kasumi-san also needed to leave, and she called Tomo to help her pack. When the business was done, Kasumi decided to celebrate with a can of beer and offered Tomo to join. Getting a bit carried away over the boozy sit-in, the main character lost his composure at the sight of Kasumi's erotic body; his long abstinence broke free, and he threw her to the floor and began to caress the girl's lush curves. It turned out that she was not against it at all, but rather encouraged his actions, then Tomo's brakes completely failed, and it ended in stormy sex.
In the morning, Tomo was depressed by what he had done, but contrary to expectations, before leaving, Kasumi encouraged him and said that if he let more of his male nature out, he would have many pleasant moments ahead with Ayu-chan and Sayu-chan. Stunned by such words, Tomo still hoped to control himself, but no such luck when the older sister literally molests him and teases; what's the point of holding back, "it's a sin not to drink when at the well", Tomo decides in anticipation of fun days with his hot sisters... @Anitokyo