The Ragnarok System of the Desperate Reincarnated Demon Lord and the Seven Aggressive Maidens, Vol. 1 - Kenji Saito

Love, war...and reincarnation!!Rintarou, a renowned hero who helped save Japan from being overrun by demonic monsters, has become a socially awkward university student! Though he still has his incredible abilities, there's one thing he doesn't have--a girlfriend. But one day, a princess suddenly approaches him and asks to be his wife, his girlfriend...or even his friend with benefits...?!