実は血の繋がってない姉と弟が両片思いだったら、くっつくのは時間の問題だと思いませんか (Associated Names)

The protagonist, Haruhito Ishimoto, a second-year high school student, lost his parents in an accident. Now, he lives alone with his 24-year-old sister, Kinoka, who works to support him. However, Haruhito harbors feelings for Kinoka. Upon discovering that they are not biologically related, he struggles with the moral dilemma of whether or not to confess…