Transmigrated as an Extra, I Redeemed the Mad Emperor

[Transmigrate into a book / fictional ancient setting and court intrigue / adored by all / bottom] Su Yu buys an old book at a market. While reading it, an accident sends him into the story, where he becomes a minor character with the same name. The catch is that the book is unfinished, so everything is unknown to him. The male lead he saves in the great hall is nothing like the useless person described in the book, and the fellow traveler who suddenly appears has a far from ordinary identity. A few days later, he suddenly notices something strange. This novel isn’t an ordinary novel at all... Worst of all, the person he hates and fears most has transmigrated into the book too...