The story begins with Souhei, a second-year high school student, who lives with his little sister Umi. Umi is extremely cute and popular among her peers, but she's also very clingy and flirtatious towards Souhei. As the series progresses, Souhei tries to maintain a normal sibling relationship with Umi while dealing with her over-the-top affection.
It falls under the Hentai category, specifically focusing on "Onee-shota" (older sister and younger boy) dynamics. Availability and "Links" uchi no otouto maji de dekain dakedo mi ni kona link