Snake Evolution System - Chapter 32 - Athena The Keeper Of The Tomb

A skilled but unfortunate modern-day assassin was killed in a freak accident. However, he soon found himself summoned to another world by an evil wizard, who had him possess the body of a boy as an experiment. After successfully planning the evil wizard’s downfall, he used the wizard’s body as a springboard to gain influence and power in his new world.

- Description from Novelupdates

For non anime fans- Yandere is extremely possessive girlsIn an open world MMORPG game called Stellaris Fantasia Online, me and my partner we're rising to the top, killing other players, farming loots and so on....But, yes, this partner of mine won't let me play with others.... even with my friendswhy? because she's a Yandere....Its so irritable that I unfollowed her.... well that decision hurts me too, since she might turns out to be a hot onee-san (older woman)But as soon as I attend the class, my homeroom teacher is in bad mood...Why??Just read the title....

Waking up, I discovered that I had become a cat with superpowers...