Toaru Majutsu no Index SS - Volume 2, Chapter 5: What is it That the World Lacks? The First Friday of April.

The hidden dragon stirred from its sleep, the fierce tiger descended the mountain! Ye Wudao, following his master's orders, crossed into the mortal world, his medical skills so advanced they could reverse fate, his divine magic alone dominating the universe. Whoever dared touch my dragon scales, regardless of their power or status, was met with instant death!

On a certain day, a certain thought came to Japan’s Sun Goddess. ——Aren’t there too many Japanese people being abducted to other worlds? It’s true that the large majority of Japanese are diligent and docile and soft-hearted, which makes them pretty much the best people to ask for favors. “But recently it’s just gotten way too out of hand…… Oh, I’ve got it! Whenever a Japanese person is summoned, I just have to summon an otherworlder!” And now, every time a Japanese person is summoned, princesses and elves and beastmen and whatnot are reverse-summoned. Under the acknowledgement of the government, they begin living in Japan. Today, too, Japan is at peace. And so begins this laidback isekai cultural exchange story♪

[Power System has beautiful Waifus as his spirits.]

[Read for the great plot and a perfect HAREM. There will be SMUT chapters only when required. The protagonist isn't Naive and treats his woman with care.]

[Read only if you want a great plot, sweet romance, a perfect harem, and good smut without any forced development.]

[Story would make sense as you progress I have avoided info dump and explained in a natural way to answer each question through the characters.]

*Ding!*

[Dual Cultivation System installed]

…

Yue Yan Gets kidnapped by the goddess on his sweet night with his girlfriend. She asks him to help her on a mission against the XieLong temple but he turns her down.

Later, some mysteries reveal their past and Yue Yan agrees to help her in order to meet his Bing'er again who has also been sent to the new world.

When he transmigrates into the body of Meng Long, he finds out he has a special Physique, the Supreme Yang body that stops his growth in Cultivation unless he Dual-Cultivates with a woman.

Yue Yan's new family had mistreated his predecessor Meng Long so he decides to leave the clan to embark on a new path with his beautiful concubine Xue Rou.

Join Yue Yan AKA Meng Long, in his Journey to reach the pinnacle of the world.

“Jiang Yu transmigrates into a novel and becomes a side character in the book.