Uh just because its not "right" in your country doesnt mean its weird everywhere else. I mean in my country its normal to have sx at 13 (you can give consent anytime) and no one says a word about it. In that case i also have ick about being V after 18, most people here would also laugh at you for it. So if you dont like it dont read it, simple right?(づ ̄ ³ ̄)づ
And like I said if it would be "legal" you and anyone else would most likely be taught that its normal, therefore yes, it would be okay. If you had a child, its the same as getting white sheet of paper. Now you write on that sheet, their first words, acts and so on. And childred trust their parents the most, so if you taught them to kill, they would in fact kill thinking its okay. ( ̄∇ ̄)
A lot of people have mentioned this but yeah, it does give me an ick, the fact that she's still a minor while the guy is a full grown adult. I just imagine that she's 18 so that I can continue to read this coz the art style is so good and I love Namaikizakari sm. (I try to filter things just because this is fiction but if it's irl, it's without a doubt that an adult dating a minor should not be tolerated)