Toaru Majutsu no Index - Volume 20, Chapter 2: The Beginning of the Invasion and the Counterattack. Angel_Stalker.

Read the first chapter. You will probably like it. ;)

The 27-year-old Wei Han is a slightly fat, slightly chicken-livered, and slightly foolish, pure-hearted and besotted top, and his sweetheart who had been together with him for seven years, in the end, was stolen away by Qi ZhiFan one morning.
Deeply broken-hearted and in despair, he went overboard with binge eating, and ended up pathetically choking to death…

By accident, Lu Zhiyu found the entrance to a low-dimensional world, and thus began a totally different journey!

Free to control everything in the low-dimensional game, Lu Zhiyu felt like a gamemaster, and even God.

- Description from Novelupdates

There was a man in the modern world that built his business empire from scratch. He was hailed as a genius by his peers and was respected worldwide due to his contributions to the world.If it is not only for that unfortunate accident that led to his death. He was a man who could potentially change the world with his mind that still stores a plethora of ideas.But—fate had others plan with him. He found himself in another world, what’s more, it’s primitive and technologically backwards compared to his last world. And what’s more, he turned into his younger self, and in this world, he was an orphaned boy.For him to survive, he must use everything that he had at his disposal, and that was all in his head.