Alright, since there are 2 children - either twins or 1 child cloned - I'm now completely sure one of them is Maru and Maru needs to find the other one. Still wondering why, but we might need to wait and see their powers. Usually in similar stories "big mission to reach a person" is necessary because the person in question is very dangerous, very powerful or "has potential to save us all", so I'm looking in that direction with one eye.
Also, it's all confirmed about Hiruko being kids if anyone still doubted that. And since they were all called Hiruko by the AI and Maru was just born at the moment, he must've learned this word from somebody else. That would mean that either Mikura or whoever took care of Maru in his first years was ONE OF the Academy's children.
I wonder just how much Sawatari and Aoshima knew about "the heaven plan". Like, they seemed to have some idea what's going to happen, just not exactly when, while the technicians were kept completely in the dark. Is there an actual post-apo outside of their facility? Is there some global war or radiation?