Demons' Crest

When sixth-grader Yuuma Ashihara and his classmates log into the VRMMORPG Actual Magic, reality and the virtual world violently merge into a terrifying new landscape. Trapped in chaos, Yuuma is suddenly confronted by his classmate, Seumika Watamaki, only to find that she's twisted into some sort of bloodthirsty monster. Will Yuuma survive this horrifying new world, or will he fall victim to the Crest?

(Source: Webtoon Entertainment)