MTL - Urban Banished Immortal - Chapter 19 Four Harms Reunited

Another entry in what you can call the Proto Harem Series: the books written before the Harem Series that take place in the same world.

It’s about a swordswoman whose student is captured, so she goes to rescue her.

Matthew, a 25-year-old otaku, never imagined his obsession with fantasy worlds would turn into reality—until a fatal gas leak ended his life and transported him to another world.But this wasn’t the second chance he hoped for. Born as the illegitimate son of an affair, his very existence was a stain on his family’s honor, and his father relentlessly sought to kill him.Yet Matthew, now Claude, survived, again and again, driven by an unyielding will to live.Until one day he discovered his power darkness. Feared and reviled in this world, dark mages were hunted and burned alive.Knowing his gift could become his downfall, he trained in secret under Theo, his true father.When he turned sixteen, he, his mother, Dalia, and Theo planned their escape from the small town.But their attempt was thwarted by knights and clerics from the Promised Land.Though he narrowly escaped with his life, the cost was high—his family’s safety shattered.Wounded and desperate, Matthew fled to the fabled Elysian Plains, the last hope for those like him.Just as he reached the border of the Elysian Plains at eighteen, an ambush left both him and his mother gravely injured.Collapsing on the sacred ground, he heard a voice echo in his mind:[Welcome to the Elysium of Darkness System, Lord of Calamity.][Your first quest is available!][Increase the number of dwellers in the Elysium using your seeds and blood! Spread your legacy by making demons and witches bear your children!]

Wyatt Jacob, a young man who hated the profession he once loved as a marine biologist after being brutally castrated and sexually assaulted by a pod of dolphins, had lived his life with pain and suffering as an impotent man having no other choice than to continue his work as a marine biologist with the emotional trauma that now accompanied it to earn a living.

But that was until he met the 'Happiness god' who granted him the chance to be reborn in the 'World of Tharcania'. A world filled with wonders and mysteries as 'a pirate; -'a prince exiled by his empire and thrown into the sea.

Now given another chance to live his life with his little brother intact, Wyatt will sail the seas of the 'World of Tharcania', exploring its beauty and wonders with the various pleasures that came with it.

Perhaps it is the choice of fate. As a senior otaku, Qian Lingfeng got the “steel shell system”. However, when he swept the world with the system, became a local rich man, made all kinds of beautiful women, opened a harem, and realized the ultimate fantasy of thousands of otaku, he found that things seemed far from simple!
When the end comes, biochemical zombies suddenly come down, fierce beasts are in power, bloodthirsty zerg roam to kill the world, and human lives are comparable to dirt. Where will weak human beings go in this world? Is humanity going to be extinct? Or … can an otaku save the fate of the human race?

- Description from Novelupdates