Park Danggu and you have been best friends ever since Jang Uk brings you to Songrim, you and Danggu has a chaotic friendship. Park Danggu, Seo Yul, Jin Choyeon, and Jang Uk we're the four seasons, they are a very skilled mage and they were also your friends but what everyone doesn't know except for Jang Uk, is that you were actually Naksu, the shadow assassin that everyone was afraid of, you shifted your soul into Mudeok that was a blind girl but when you shifted your soul to Mudeok, you can now see but you aren't powerful like the same as Naksu and all of that, only Jang Uk knows about that

Suddenly Jin Mu who was the leader of Cheonbughwan who was also the one who teaches you how to be a powerful and dangerous assassin but somehow, you didn't know it was Jin Mu all along because the one who teaches you back then has his face covered, Jin Mu used you (and others) for his larger goal of gaining power through illegal soul shifting and disrupting the balance in Daeho.

Jin Mu eventually figures out that you were Naksu in a different body. Jin Mu uses soul-shifting bells—a magical item that lets him manipulate soul-shifted individuals. These bells essentially put you into a trance, overriding your will and turning you into a puppet assassin. As Jin Mu suddenly forced you to kill someone that was Choyeon's dad as you can't control yourself and killed Cheonyeon's dad as Park Danggu heard this and tried to stop you, instead you just suddenly hit him with your sword on the shoulders as Park Danggu was shocked why did you do that, Jin uses the bell that affected you in a crucial moment to force you to go on a killing spree, despite you trying to fight it. It’s heartbreaking, because you loses control and ends up harming people you care about, especially Park Danggu

"Mudeok what is wrong with you!?" Park Danggu suddenly shouted at you as he saw some black spots on your forehead but didn't know what it means, he also don't know you was losing control of yourself.