These are high school DxD that I have read, and highly recommend it. Grammar are pretty good. Interesting plots.
DxD:Multiplayers
By-SpatialPhoenix
FanFiction.net
—————————-
A Turk in DxD Game
By-TurkishBoy
FanFiction.net
—————————
Timeless Conquest
By- Rain Sennin
FanFiction.net
—————————-
A Hero Journey
By-HolyKnightsofTheRoundTable
FanFiction.net
———————————————-
Dxd:Codex of the Universe
By- flameclawsxxx
FanFiction.net
————————————-
HSDxD: The Power of Wildcard
By- Authorian
FanFiction.net