User blog comment:Genista882/Mitsuru and Kokoro/@comment-26567684-20190504235406/@comment-38094676-20190505051156

They have limited vocabulary at that time, and perhaps the only word they have for a male parent is 'papa'. They were working hard to find the means to survive, I'm guessing that by the time they were free to have leisure, as in find a name for Ai, the 'papa' has stuck. >.<

It could also be the writers trying to 'undo' the negativity of the word by showing the parasites what a true father is, and I'm glad MItsuru delivered, whether he knew it or not.

I've always wondered why Mitsuru missed Ai's birth. I've read some reactions that they thought that something went wrong at first because of the crying women, I guess, the writers were going for that bit of suspense?

But, I'm sure he didn't miss the birth of their next children. It's just so out of character for him to miss something this important unless there's a good reason to...or maybe a poor one, like the women forgetting to inform him because they all got scared and nervous when Kokoro went to labor. UGH!