I'm the Hero, But the Demon Lord's Also Me, Vol. 4 - Akiyoshi Ota

As Yuuma's battle with Carina rages on, he struggles to master his new swords. Fortunately, his demon sword has a mind of her own, and she's doing the fighting for him! But he's also got a secret move, and after he unleashes it on Carina, she finds herself getting a little hot and bothered... Join our hero (and demon lord) one last time in this pulse-pounding conclusion to the series!