Ane Log: Watashi no Otouto wa Natsu ni Kaihouteki ni Naru Hentai de Aru Sister's Log: My Perverted Little Brother is Open Minded in the Summer
The manga's story centers on Moyako Konoe and her younger brother Akira. When they were younger, Akira proposed to her, so Moyako thinks he is a pervert who has fallen in love with his older sister. Moyako's misunderstanding leads her to create wild delusions about her brother.
[Source: Anime News Network]