Now I'm a Demon Lord! Happily Ever After with Monster Girls in My Dungeon: Volume 10 by Ryuyu

Reborn as a demon lord in another world, Yuki is currently helping Lefi think of ways to fight now that she can’t revert to her original dragon form anymore. After a bit of brainstorming, she succeeds in Dragonizing herself by covering her entire body in scales, thus strengthening her human form! With that task complete, all that’s left for her to do is train.

Suddenly, however, Yuki receives a distress signal from Nell. He rushes to her side, only to find the Elvish Enclave under attack by the fiends, who declare war on the alliance of elves, demons, and humans! At long last, war breaks out between several nations! Yuki joins the battle in order to protect his family in the dungeon, but what awaits him and the others?!