Who is 'He'? | AU | FMA:B x GC

This is an AU i randomly came up with the other day. I'll probably explain it as i go.
It also didn't turn out how i had originally wanted it, but that's ok.

[@nyx_wildshadow]

I randomly found this video and now I'm very interested in what this AU could possibly be. Yes I realize this is a year old.

[@justabicerrado.5362]

Wow