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Aoichan asked a question

Please help me look for a manga. The story goes like this. The pair are childhood friends and they are madly inlove and i think majority of the chapter was just all about sex. I remember a particular scene wherein the sister, who is also very supportive of their relationship, peeked through the door and saw his brother had sex and was delighted to see it ( i cant remember in detail). Heeeewlpp