Hopper1 is composed of many mysteries, no thanks to canon not actually establishing things like how old it is, whether all the Chemies are actually from Japan/made by Japanese citizens, things like that.

I think Rinne would be interested to know how Hopper1 (and steamliner) met Hotaro when he was younger (I would like to know that too toei!)

Good question! Was that portal dropping Houtaro in the Ouroborous Realm their first meeting, or were there other occasions?

there's so much to think about!