Is It True That I Can Be Stronger If I Make Love the Devil's Daughters?

Orphaned after the murder of his parents, Uta-Rain is eventually auctioned off as a slave. Desperate to be treated badly again wherever they take him, Uta awaits…… Surprisingly, he was awaited by a magnificent meal and five beautiful older sisters. But they are the daughters of the Demon King, who was defeated by the hero 16 years ago….!?