There's no incest or pedophilia... Spoilers...
Naru is not blood related to Mei - he has watched over him from the time Mei was born (yes, it's weird) and loved him, but not like that. They had very little contact throughout the years, almost 0. Naru doesn't make a move on Mei. Mei starts pursuing Naru when he's 21.
Sorry but still against my morals, Even in the face of Society or Law Naru is adopted legally which would mean Mei’s father is he’s brother so Mei is his nephew aside from that there is 17 yrs gap SEVENTEEN like i cannot even if Mei is an adult but he’s still 22 (i am 22 and what i feel reading this its like dating my Dad) which so weirddd i just cannottt ASIDE FROM THIS he practically raised (which he said that he loves him and watch him grew up he said that) him he saw him grew up this make Naru’s character a Groomer, Pedophile, and Incest. I cannot normalized this huhuhu

When I said I wanted naru's story I didn't mean this
Was is really necessary to add incest and pedophilia