Satan 666 (The God of High School) vs Fiamma & Gabriel (ToAru)
Ngl, Complete Holy Right getting ganked by Touma's demon hand thing makes me expecting Fiamma power to be much lower. Especially since he hasn't appeared much in later novels from what I heard?
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Getting punked by debatably one of the strongest entities in the verse (albeit it wasn't at that level here to be fair) is hardly an anti-feat.