Surviving As An Extra In Fantasy World Isn't Easy - Chapter 3 :Crisis

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

Ryu Han-bin, the main character who fell into a new world after being chosen as a ‘suitable person’.

Because of the error in the guidelines, the training is repeated endlessly…

With a marriage contract forcefully done, he married her, and all she could do was comply, and resent him deeply for that and for all the following misunderstandings they faced.
However, it was already too late when she understood she actually loved him.

Traveling to the world of Hokage, Kamiyo Colt witnessed the chaos of the Nine Tails firsthand.Without any special powers initially, he planned to develop quietly and survive until the Infinite Tsukuyomi. However, when he first trained his Chakra, his system finally activated.The system's rules were simple:By healing others, he could gain random attributes and skills.“Heal Uzumaki Naruto to receive pure Ashura Chakra!”“Heal Uchiha Shisui to gain his bloodline talent!”“Heal Sasuke Uchiha to obtain pure Indra Chakra!”In this way, Colt steadily developed his abilities over more than ten years.During the Fourth Ninja World War, when the ninja coalition saw him suddenly knock out the Six Paths Madara with a single punch, he looked innocently back at them.“What? I'm a medical ninja. Doesn't it make sense to defeat him with one punch?”