It's a story that's js a tiny bit complicated bc our MC isn't able to differentiate the love she feels towards her sister , unfamiliar on whether or not it's romantic love or familial love, but she never act on the love itself as romantic, crossing her sister's boundaries.
Now MC and mamiya's love are a quiet one, it's more so like a comfortable love that takes its pace and isn't aggressive, which is a rare kinda relationship in the romance genre.
The people who's freaking out in the comments are insane imo this story is so unproblematic that it's weird people are even fighting abt it.