You've Got Mail: A Cautionary Tale - Chapter 53 - Come, Come Touch Your Belly (NSFW)

Liola—the best assassin in his world—has vowed to kill no more. He was being chased by an assassination organization when he accidentally dropped into a parallel universe: through a dimensional gate and into poor teenager Kaiser’s apartment. Instead of going to the government shelter for lost dimensional travelers, Liola and Kaiser wind up going to school together.

Liola has been trying his best to live the life of an ordinary person, but after certain things happen one after the other, he begins to realize that being an ordinary person could be harder than being an assassin.

In a magical medieval world, it's difficult to hold on to one's beliefs... even maintaining one's integrity is a challenge.Because the commoners here are not simple; they are ignorant, greedy, and cruel.Because the nobles here are not noble; they are insidious, ruthless, and tyrannical.However... not all human constitutions can be generalized.Lann touches the two hearts and three lungs beneath his chest.He estimates that not only in this world but also in the other worlds connected through the convergence of celestial spheres, he can maintain a healthy sense of morality.—And then get rid of all the incorrigible scum!

Previously one of the ten greatest Martial Emperor, Gu Feiyang somehow died near the mountains of Heaven Wave.

Fifteen years later, Gu Feiyang crossed through the cycle of rebirth. He was back! But this time, he was in the body of Li Yunxiao. Since then, Li Yunxiao started a treacherous journey. The world is in turmoil once more!

- Description from Novelupdates

The protagonist fell asleep while playing an online game. However, he awoke in a strange world with his game character’s appearance. In a state of shock, he noticed that he was equipped with nothing but his strongest weapon and armor. To make matters worse, our hero’s appearance was changed by the special avatar skin『Skeleton』when he entered this new world. The protagonist wanted to live without drawing attention, but he got acquainted with the dark elf Ariana and received her request.