Mr Gu's First Doting Marriage - Chapter 437 - 438: A world without you is hell for me

Yuki, a high school junior, dies heroically saving a stranger and is reincarnated in a fantasy world, where he discovers an extraordinary and unrivaled power.

Witnessing her boyfriend cheating on her with her bestie, Shiyao was so angry that she went to a pub for fun and met a man, who was really a piece of work. After a crazy night she fled away, but was embarrassed to know that the man she slept with was her boss You Ze.
Jesus, give her a break!

- Description from Novelupdates

Naofumi Iwatani, an uncharismatic Otaku who spends his days on games and manga, suddenly finds himself summoned to a parallel universe! He discovers he is one of four heroes equipped with legendary weapons and tasked with saving the world from its prophesied destruction.

As the Shield Hero, the weakest of the heroes, all is not as it seems. Naofumi is soon alone, penniless, and betrayed. With no one to turn to, and nowhere to run, he is left with only his shield. Now, Naofumi must rise to become the legendary Shield Hero and save the world!

After getting shot, Lucas, a serial killer, reincarnated into the novel world as a tragic villain with the same name, Lucas Ciffer.

Lucas Ciffer was supposed to be the Holy Kingdom's successor to the throne, but his demonic appearance and the powers he possessed terrified the entire kingdom. A white-haired boy with red eyes and pale skin, together with his dark powers, got persecuted and exiled by his own family. Not to mention that in the future he was destined to die by the hand of the hero.

Lucas fell from holiness, and, with the serial killer's bloodlust and knowledge of the future, he decided to prove the world right.

Yes. I could be a villain; no, in fact, I WILL BE THE VILLAIN.