Eh I just think his sister is cute and that the yandere is oddly stimulating.. attractive?
Anyways a different world does imply different genetics. The common sense aspect is something the MC really should've paid attention to.
Even if his father perhaps failed to tell him, all the signs...
I like isekai sometimes. Although it's a cliche but they're often cliche for a reason.
I actually do like this one but more because it reminds me more of the themes of society in Korean novels and manhwa.