The Strongest Wizard Becomes a Countryside Guardsman After Taking an Arrow to the Knee - Chapter 402 - The Lord of the Undead

When she woke up, Lake returned to the classroom of the third year. The classmates were in class with swords and sticks, and the teacher became a female Taoist.
The little fat man in the back seat, how to put two big hammers under his chair.
Rick found this to be a global era!

- Description from Uukanshu (translated)

Dani was just an ordinary high school student—until fate played its cruel hand. After losing his parents at 15, he was left alone in the world with only money to his name. Neglecting his health, he developed cancer, and while waiting for death in a hospital bed, he found solace in novels, manhwas, and manga.He often cursed the weak romance in harem stories, where the MC had power and a harem but did nothing while the women fought over him. But one novel captivated him—a masterpiece about 100 heroines, each with tragic pasts, rising to the top of the world. It wasn’t about an overpowered male protagonist but about the struggles and triumphs of these heroines.“If only I could transmigrate into this world and marry them all...”Then he died—and woke up inside the very novel he admired.But not as the protagonist. Not even as a major character.Instead, he is reborn as Dani Everhart, one of the many sons of the king, a forgotten prince with no real power or influence. He is wealthy but not a contender for the throne, overshadowed by his brilliant older brother. However, he has one advantage—his knowledge of the story.He knows the heroines' hidden pain, their struggles, their tragedies.And he refuses to let them suffer.With no grand ambitions for power, Dani sets his sights on a single goal—to make each of these women fall in love with him, forming the greatest harem the world has ever seen.But as Dani gathers heroines by his side, his actions begin to change the story itself.And soon, the world will realize—this forgotten prince is no background character.He’s about to rise.

One day, Luo Jian woke up from his sleep and found himself in a locked chamber where the door and window were all sealed. A note with a few lines written on it was tacked to the wall: “Escape from this room within an hour, otherwise, you will die.”

There is a sequel called Reincarnation Night (轮回之夜) that takes place in the same universe but has different main characters

- Description from Novelupdates