The Reincarnated Assassin is Genius Swordsman

The infamous leader of the assassins known as the Shadows, Raon.
I had lived my entire life as a dog on a leash. However, through a twist of fate, he obtained a new life—as the grandson of Glenn Zieghart, the Destructive King of the North! He prepares to use the Ring of Fire he still possesses as an infant to begin cultivating when he’s diagnosed with the Curse of Frost. With the odds stacked against him, will he be able to finally stand on his own feet and live life by his own will, to become the strongest swordsman on the continent? “I will slay anyone standing in my way of revenge…
even if it is a god.”

Note - translation work
Author - writingant ( there are many fakes with the same name
Source link - 환생한 암살자는 검객이다

장편 판타지 소설 앤트(Ant)가 집필한 장편 판타지 소설
I use kakao

{ its original novel not a fan- fiction but as it's a ftl )