The story starts with only ecchi-like and some boring sens until it gets to volume 7 or 8 were it becomes a master-piece .
I don't say the first volumes were a bad shit but I give them like 7/10
here where ecchi,comedy,romance and epic action gather with mixture of devils,fallen-angels and angels with the most important creator the dragons .
just enjoy reading it.
it fellow hyoudou issei a pervert 2nd year school boy whom was killed by his first GF Ranyare that appeared to be a fallen angel and he was reincarnated as a Devil by the Master and high-class devil Rias Gremory to become her pawn along with the rest of the team (akeno,koneko,asia and kiba...) and other characters to get along after .