My Fenrir System: Heir To The End - Chapter 22: Selling manna stones

Corporate slave Alexander dies with only one regret—not finishing the fantasy novel in his hands. Fate has a twisted sense of humor when he awakens as Alexander Flamingo, the perverted villain destined to be expelled and killed in that very story!Armed with complete knowledge of the original plot and a mischievous “Harem King System,” Alexander plans to rewrite his fate. No longer the one-dimensional pervert of the novel, he'll use his future knowledge to manipulate heroes, seduce heroines, and rise from disposable villain to the true mastermind of this world.The system grants him power through every relationship he builds—but can this calculating reincarnator use his second chance to avoid his predetermined death and become the ultimate Harem King? One thing's certain: this story won't follow the original script.

A chance to change, to challenge destiny, making dreams a reality, and live a legend! A regular man gains a system that allows him to turn into a fish!

- Description from Novelupdates

A modern university graduate, traversing the window between two worlds, steals a celestial cultivation opportunity that originally did not belong to him. And this celestial technique, quite unorthodox...My credibility should be assured. In order to be responsible to the readers, I must earnestly remind you: my book is easy to linger on in your thoughts, so proceed with caution.

Sure, the world is ruined, but I’ll live my own way. Of course, luxuriously and gorgeously.