I found this story through a scanlation site a while back. It's a pretty straightforward slice-of-life manga, so the character list isn't super complex, but it's all about the dynamic between them. The main focus is the little girl, Nao, and her 'Mama,' who is actually her older sister, Saki, raising her after their parents passed away. The core is watching Saki struggle but pour so much love into being a parent, and Nao's childish misunderstandings of the situation.
Beyond them, there's the kind neighbor, Mrs. Tamura, who helps out sometimes, and Saki's friend from college, Rina, who provides a bit of an outside perspective on how hard Saki is working. There's also Nao's kindergarten teacher, who notices things but is gently supportive. The story doesn't really have villains; the conflict is internal and about coping with loss and building a new family. I remember a chapter where Nao draws a family picture with her, Saki, and their late parents, and Saki has to explain it to the teacher. It's those quiet moments that define the characters more than any big plot twists.
I think the author does a good job keeping the cast small and intimate. It makes the emotional beats hit harder because you're not distracted by a dozen side plots. Sometimes you just want a story about two people figuring things out, and this one delivers that warmth without needing a huge ensemble.