I don't actually watch a lot of Jerma, I just see some of his videos when my sister watches him. But here's my ideas based on what I know:

-Otto is a teammate
-All buffs and debuffs are dealt in 2s (+2 speed -2 power ect ect)
-Bugleberry is a shop keep
-The final boss does Safer Sephiroth's 'Supernova' move but it's the jerma meteor and all the jerma planets now
-It's not an isekai, Jerma is just a streamer in an RPG world cause why not?

Also it's hard to tell but the gun part of his gunblade is based on the Scout's gun from Team Fortress 2?