Mamagoto: Shougakusei Mama to Otona no Musume

Yuzu Okashi is a shut-in author living alone in neglected squalor. When the neighbor girl Makoto forgot her apartment key, Yuzu took her in until her mom got home. When Makoto saw the mess in Yuzu's apartment, she promised to take care of Yuzu like a mother should!

(Source: Sqare Enix, translated)