I'm the Hero, but the Demon Lord's Also Me manga volume 4 features story by Akiyoshi Ota and art by Tatsuya Endo.

The hits just keep coming for Yuuma, as a "slightly racy present" arrives for Alfin and Lavinia from another world, and inside lies a secret capable of altering the fate of the world...! Don’t miss the thrilling conclusion of this pulse-pounding (in more ways than one) fantasy!