Plot-wise this is feeling pretty generic for me. I liked when Hikari joined as another person for the main two to interact with, it seemed like there were more opportunities for interesting character dynamics, but the sister introduction is feeling kind of generic again. I'll keep reading, but I'm not super excited about this one.
Ok, so I'm not the only one with that impression. I tried giving the series a go but it feels like the author thought out the whole story but didn't bother giving it some... pizzaz? I don't know how to explain, but it feels like they're just going through the motion and the whole thing feels generic.