My Blood Refinement Technique

Sylvan's a young man who is just trying to make it through university. One day his soul is summoned to another dimension by a magic artefact a trash mage got by chance when leaving his academy.

However he also summoned a demonic cultivator called Zou Yi who ends up resisting, killing both the trash mage, Angus, and Zou Yi in the process. Leaving Sylvan in control of Angus's body with both Zou Yi's and Angus's memories.