Zero Damage Sword Saint: I Enrolled in a Magic School and Wound Up in a Contract with the Demon Queen: Volume 3

Even when history's biggest failure succeeds, trouble still finds him! Having defeated the legendary Demon Queen and proven his strength to the entire continent, Eugene receives a letter from his father, asking him to come home to the Grenflare Empire for a visit. Though Eugene expects a quick and casual trip with his girlfriends, Sumire and Sara, it takes an unexpected turn when the seal on an Infernal Demonic Beast that almost destroyed the imperial capital a century ago suddenly breaks. Eugene has no choice but to do what many thought impossible: He has to slay the creature! And the key to doing so lies in none other than...an ancient Mana Link technique he has to use with his two girlfriends?!