Crimson Overlord - Chapter 1: The Young man with Crimson Eyes

A teenager named Evan Mason was reincarnated into the magical world of Harry Potter and goes to school at Hogwarts!
With only his knowledge of the future and great talent for magic, he takes the path towards the top of the magic world, only to realize that ever step he took, changed everything!

- Description from Novelupdates

Indra (5) grew up in her family while being shunned and ostracized. When she regained the memories of her previous life, she decided to run away from home and thus trained herself to absurdity.

During her training, she encountered the young adventurer Sword, who looked just like a middle-aged guy. Worrying about the impertinent, eccentric, pointlessly strong young girl, Sword invited her to go on a journey with him.

Meet Baek Ri-hyun, the renowned legendary martial artist of murim and was given the title Martial God.In a battle against the Heavenly Demon who has transcended mortality, Baek Ri-hyun was suddenly pulled by an unknown forces to bring him to another world by the power of a goddess who is in need of help from different people, not knowing she pulled a god into her world.Blessed with a system to aid the growth of the future heroes, I don't think he'll need something like it as he ventures the new world.

The most feared Assassin in the world died because of vengeance.