Death March kara Hajimaru Isekai Kyusoukyoku (WN) - Book 1 - 1-5. Fortress City Life Begin!

Xie Jingyuan, the master taoist of Qingxu Temple, was reborn into modern times together with the cat demon Su Miaomiao.

Su Miaomiao: That classmate’s dried fish seems delicious.

Xie Jingyuan: I’ll buy one for you, don’t steal it.

Su Miaomiao: It’s raining, Taoist Priest, come here and pick me up.

Xie Jingyuan: I’m busy.

Su Miaomiao: It’s okay, a male classmate is willing to drop me at the dormitory.

Xie Jingyuan: … Send me the location. ·

- Description from Novelupdates

As a promise, he went out into the world as an assassin. 3 years later, after becoming the Supreme Assassin, he gave up on everything he had and returned to the ranks of ordinary people. But one day, Kismet, a mystical game created by the National Research and Development had appeared.

Enigmatic hands, spectral frame, and one cunning strike just like the swing of the Grim Reaper. The Supreme Assassin takes on the mystical world, and how his legendary tales sets off, progressively ascending the altar to becoming the best.

- Description from Novelupdates

500 years ago, Chen Xi was devoured by a crack in the void and was transported into a cultivation world.

After the ‘100-Year War’ between the Necromancers and Priests, an all-time genius who’ll shake the power structure was born. “Am I a rare case or something? Do I have talent?” A potential beyond all imagination. He obtained his father’s undead army and entered the great Necromancer school of Kizen that divided the continent. Geniuses are geniuses, even when gathered among the elites. The research community was flipped on its head by the appearance of a new case. Professors wouldn’t leave him be alone, wanting to make him study directly under them. Officials from all over the kingdom and heads of organizations fidgeted over whether to scout him. “Professor! When can I make a Lich?” “Gimme a break. How talented are you? You’re crossing the line, honestly.” A genius among geniuses had appeared.