Oshi no Ko

[Kraco]

The father could be a married man and his wife is a yandere. So, the father might have just been super careful and thus not willing to meet the kids, lest the scary wife finds out. She found out anyway and arranged Ai's murder.

I don't really believe this theory to be it.

[DarthEnderX]

The father could be a married man and his wife is a yandere. So, the father might have just been super careful and thus not willing to meet the kids, lest the scary wife finds out.

That would still mean the guy cheated on his wife with a teenager. Which would make him still a total asshole.

It's true that Sarina and that Doc reincarnated as Ruby and Aqua... and being able to hold a high level discussion at 2 or 3 years of age is already un natural.
But somehow they've kept the supernatural limited to just that, some arm twisting for the pitch and keep a shorter timeframe for the story.

I'm honestly surprised that the fact that Aqua is a fully-trained doctor hasn't been used more. You'd think that would have uses.