You know what, after this chap I feel like the ominous feeling of this manga is slightly diminishing. The way I view it right now is that the story is pushing the narrative of how to work a huge age gap relationship that is almost viewed as taboo in society nowadays (or maybe it is, since it's almost impossible to find this kind of stuff and not think that it relates to grooming) in a wholesome way. The girl is no psycho, she's not mental nor yandere, and the mc is not being manipulated at all, he's just dense just the way most protagonist are, the vibe is totally different from that "Okaeri Papa" manga. This shit is actually pretty cute not gonna lie and sister is based as fuck for that, totally stand with her. Now what's left is how will the author deliver this kind of story and stay in the wholesome route while overcoming adversaries from how society sees this kind of relationship itself.