Harry Potter: Eclipse. - Chapter 75:

Born with the fate of a slaughterer, but all he wanted to do was help.

Worlds overlapped, and Alien Species descended.Strange entities emerged one after another, as the shadow of evil spread wildly.The calm of life was shattered, and Zhang Xiaoman, inside a fish's stomach, accidentally consumed a system named “World-saving Plan”.From then on, he became the only person among all humans with Extraordinary Power.…Inventing an ancient oath, he established a unique methodology, Cultivated Dark Energy, founded an organization, took Control of the Transcendent, and resisted invasions.Well, this is actually the story of how a Big Con Man bluffed his way into saving the entire world.PS: Contains elements of the behind-the-scenes, Cthulhu mythos.

Protagonist travels between different anime worlds to right wrongs and uncover his reason for being along the way.

- Description from Novelupdates

“You will hear many of his Death Eaters claiming that they are in his confidence, that they alone are close to him, even understand him. They are deluded. Lord Voldemort has never had a friend, nor do I believe that he has ever wanted one,” Dumbledore told Harry Potter with absolute certainty.But what if Voldemort did have a friend? Not just a friend but the friend? A millennia-old wizard, who learned the secret of Hogwarts from the great Four founders, and had his own goals to take over the world?To stop that ancient wizard, an ancient power is called upon . . . in the form of a girl. A Muggle-born at that.Christina Norton has powers beyond anyone's imagination but she is too caught up in the Chosen One Harry Potter's life and catastrophes. But as she starts to uncover the plans of Voldemort, she realizes someone else is working with him. Someone who wants her dead. Why? She doesn't know. She just knows she has to save her loved ones and Hogwarts from Malgino and for that she is ready to go to the end of the world.And fight whoever comes in her way.