Ok so I came up with a theory, as a hsr fan who hasn't played the game but is following the main story, that...
Aha is sampo koski. (take it with a grain of salt. And don't come after me and be mean pls and thank you)
Cuz imagine this. Aha came across this idea after seeing Himeko make an imaginae of herself that is able to leave the planet, he creates one himself.
A few things I delusioned might connect dots is, one. Sampo is almost always everywhere the astral express and Mc has been (minus amphoreus but no aeon could enter it in the first place). And since aha is a good friend of akivili(? I'm not sure about this).
And Aha is banned from entering the fool's tavern. If he made up an imaginae, he could enter and sate his curiosity of the place. Very elating.
Another is him having an environmental uniqueness that no other character has (except himeko).
Anywho. That's my theory for today. Lemme know if anyone else thought about this ideas about it.
