Description via YuriNavi:

"Nomura Nao and Kyougoku Hina" is the story about two high school girls, Nomura Nao and Kyougoku Hina, who sit in the same class. Nao has always had trouble with Hina, who seems to always be in a bad mood. But one day after school, she runs into Hina who is taking care of her younger siblings. Nao dislikes her own family, but seeing Hina as a caring older sister, Nao's opinion of Hina changes drastically. As Nao spends time with the Kyougokus, she starts to learn what family is really about.