First of all never said it was insest they aren't blood related, second he clearly says he thought he was gonna be happy just watching from a far implying being in love while there was an illustration of him looking out if a hotel while the bottom had his bday as a literal child if that's not weird than I can't help you
Doesn't make things any better though although it doesn't look toxic I will give it that but the family and power dynamics isn't normal.
As a 30 year oldie if the last man on earth is aged around 21 then I will rather choose to be celibate. Because when you are around my age you think of someone in their teens and early twenties to be kids. If people who are of my age are interested in dating someone young is generally frowned upon because of power dynamics and not to mention its easier to manipulate someone young.
Yes cause he said I thought I'd just be satisfied watching from a far there being a visual of a child having a birthday after he legit fucked the child as an adult there is no other understanding of that other than romantic love. He basically says I hoped I'd be satisfied not fucking you while thinking of a child but now I did when ur an adult and am happy about it. And yes it is a me problem if you mean thinking its not ideal when someone romantically desired a child that was also a part of their family
On other hand my parents had like 2 year of age gap its my sil and brother who have whooping 7 years but when they got married my sil was 26 maybe 27 so its okay she was at her late twenties and is adult enough to make her own decisions so its alright. But some of the age gap is just wild.
There was this another bl who gave us a healthy age gap (sry I don't remember the name) mc was ml's music teacher and they meet again in class reunion where mc is 38-39 and ml is 28 so this is okay, both parties are emotionally mature and equal. It was pretty sweet bl my stupid self forgot its name.
Ya, that's really not it. He mentions, multiple times (to others and to Mei) that he loved him like family, not as a lover. That's why he was happy just to watch over him. The only family he loved was Mei's parents, so Mei is the last of the family he cared for, that's why he watched over him. They rarely every met in person - maybe once a year. It's still weird, but I imagine that's why they were able to change the relationship (if Naru had actually been there while Mei was growing up, Mei wouldn't have fallen for him and he would have only viewed Mei as his nephew - but look at Woody Allen, sometimes ppl are messed up). Naru was simply thinking about how things had changed.

I really wanna like it cause I like the author, the art and like the story concept but 18 year age gap, a dude pining after a literar child for years and that child being a son of his (if I understand correctly) step brother is just fucked. Like brother ewwwww he's legit in love with a child that's a part of his family in what world is that acceptable.