Overlord style game
It seems to me that ya'll are looking, basically, for an Epic level game (ALA D&D 3.0 - 3.5) wherein you start at lvl 21+, and find yourselves in what amounts to a Low Magic world, coming from a High Magic world. Sound about right? Given how Overlord is set, with the MC being a lvl 100 Magic User (In-game terms, probably about equivalent to 27th-30th lvl, with Epic Spellcasting as a Feat) in a world where most people, at most, get to about 9th level at the highest. ((I'm working off the 'Spell Tier' system in overlord, wherein 5th Tier spells are the absolute maximum for non-Yggdrasil characters would be about equivalent to 5th lvl spell slots, despite the discrepancies)) with magic items allowing them to exceed these limits in rare situations ((Read: The Skeletal Dragons, Dragons in general, etc.))
This sound about right? Not to mention the sheer amount of crap Momonga (The MC of Overlord) was able to bring with him, in the form of the Great Tomb of Nazarik and the Artifact-level shinoligans he was given by his guild-mates.
The question I'd have to ask, as someone who's considered running a game like unto this previously, is would this be a full-on self-insert? like with the MC of Overlord finding *himself* in the body of his character and in a world NOT the character's native habitat ((Read: Not Yggdrasil?)) 'cause those tend to get pretty meta very fast.
Other options for systems for people to consider:
BESM ((Pretty standard Anime setting system))
Mutants and Masterminds
Exalted ((Exalted in a mortal-only setting? Brutality.))