Hidamari Starlight(2019)

Hidamari Starlight

Aoi Yoneda gains a step-brother when his father remarries, but the new family is totally changed after an accident takes both parents' lives. Aoi then takes responsibility and takes care of this little brother alone. Only, on his brother's eighteenth birthday, things take an even more unexpected turn: "Please don't see me as your brother anymore." What are the limits of love?

(Source: NewPOP, translated)