
Honestly I think it doesn't matter who the mother is. That's just how it works. I think this work is pretty nice because it shows that a gay family is just like any other. You wouldn't go around asking a gay couple with a kid (or ANY couple with a nonbiological parent) who the kid's mother is, and even Towa accepts that Naguru gave birth to him (lol) So you should too. No, it's not a plot hole. It's reality.
I regret pressing the plus button on spoilers. I mean, I knew it, with what he went through but... still