Anime: I Want Harem - Chapter 42

This legend tells the tale of the protagonist, Kuroki summoned to protect the demon king from the hero.

Kuroki, unbeknownst to him, suddenly came to another world. He was summoned by the demon king, Modes. The territory which the demon king overrules was in the midst of being destroyed because of the hero. He had no choice but to bow before Kuroki.

“Please save us, Savior Dono!”

Kuroki nodded, deciding to save the demon king due to an unexpected turn of event.

Su Changqing reincarnated into a fantasy world, directly starting with a heavenly advantage, being born into a Great Emperor family.His father is Su's contemporary family head at the quasi-emperor peak, his mother is the sword pavilion's legitimate daughter with Great Saint cultivation, and even a steward of the Su family is a Saint King.Born into such a powerful family, Su Changqing could easily reach the peak just by doing nothing.But his father, Su Nan, was afraid that his son would become a pompous and arrogant wastrel in such an environment, so he established a Truman World for Su Changqing!In a poor family, with no way to cultivate, Su Changqing struggled through hardships and finally joined a small sect.What he didn't know was that his enlightenment teacher was actually the contemporary Confucian Immortal.The taciturn elder teaching him Sword Techniques was actually the Sword Fool famous across the continent.The irritable elder who always blew up the alchemy furnace was known as the Pill Saint.To prevent Su Changqing from being arrogant due to his talents, many famous teachers were extremely harsh, and the Divine Techniques taught were very difficult to master.But soon, these teachers were all panicking.“Sword Fool master, the Nine Yang Sword is too simple, is there any other Divine Technique?”“Pill Saint master, don't leave, I've already mastered the Yin Yang Reversal Alchemy Technique, teach me something more powerful.”“Hey hey hey, Confucian master, don't run, I've finished reading the books you asked me to...”Looking at the retreating masters, Su Changqing sighed helplessly,“A small sect is really a small sect, unreliable...”

Follow Chen Ming as he accepts disciples, establishes a sect, and fights his way in a world that deems him a cannon fodder.
He goes against any common sense using his wits and novel knowhow to finish missions and arm himself against his cruel fate.

- Description from Novelupdates

A 30-year-old NEET is reincarnated into the body of an otaku that choked to death on instant noodles. As he comes to grips with his new life, he realizes that this world is subtly different from Earth. The denizens of this world are far better looking, and this new world also possesses futuristic technology as well as mysterious Yin Yang masters!