Okay as much as I'm still aggravated with the ending of the AU, can we talk about how good the metaphor in it??
Might be overthinking on this but here's what I think AidaIro’s telling us through the April fools AU
As we see Kou forces and drags Mitsuba to go to the other side of the tunnel with him but Mitsuba somehow can't get out the other side. So despite Kou’s eagerness to save them both and go out the tunnel together, Mitsuba still knows there's no way he can be able to so for Kou’s sake he pushes him to the light while he stays in the dark. Because the only way Kou could be safe/happy and go back is if Mitsuba force him back to reality, a reality where Kou isn't with him.
I COULD EAT THE BITTER SWEETNESS OF MITSUKOU ANYDAY BUT AT THE SAME TIME I WANNA PUKE FROM IT