¯\_(ツ)_/¯

crying lava lamp goo

HOSol is wearing a risqué sleeveless version of that very same shirt with a black undershirt!!!!! Perhaps the sleeveless shirt is even backless, given Mori’s relative proximity to the characters of the time.

HOSol brain infestation is terminal.

Ok so there isn't any art that shows HOS without the tabard? part of his uniform or the cape thing, but there are a few where you can see under the cape pretty far so we know that the dark undersuit thing goes to his shoulders. His Overture design shares a lot of elements with his HOS design too.

With that in mind, please consider this:

But with these:

HOS is drawn so hilariously inconsistently that honestly he could have anything going on under all those layers though. It could be backless and frontless.