 If you liked
666 Satan
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 ...then you might like
Konjiki no Gash!!
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Apart from the difference between "powers" (O-Parts and "Demons") these series are pretty similar, certain characters are almost the same and deal with the same struggles through their misadventures to save the world, one way or the other. The development of the story's going pretty much the same level, tho', Gash can deliver you more and better fights then 666 can.