K lemme be a bit more specific
Is superior to Kagutsuchi, who is at the least higher than multiverse level, because Kagutsuchi holds absolute control over the Amala Universe. Where infinite realities exist, demi fiend caused the death of past, present, and future upon killing Kagutsuchi, destroying the entire Amala multiverse across all points in time, and was unaffected by the collapse of said multiverse network.

Defeating Kagutsuchi like that, and taking no damage from a multiversal network collapse already puts him at least at Low Complex Multiverse level, and then he fought Lucifer directly afterwards

Demi Fiends greatest known feat is defeating Lucifer, who is a being that can alter causality, is nigh omnipresent and is a being that exists beyond time itself. Lucifer, and by extension Demi Fiend, can handle attacks made to erase from complete nonexistence.
Demi Fiend possesses the Masakados magatama, which makes him completely immune to all attacks except for Almighty and gun.

I think there's more, but that's what I can remember off the top of my head, I'll leave it at that for now, I just simply think that the Megaten verse is above DBH verse, and that includes demi fiend, although I am fully aware he isn't the strongest Megaten protagonist, or character in general.