He is a vampire that feeds on people. He can control people's thoughts and has the ability to kill other vampires. He killed his master whereupon he drank his blood to become the most powerful vampire. Sung-ryeol became a vampire bitten by Gwi's resurrected master, and Gwi knows that Sung-ryeol will come after him. To neutralize Sung-ryeol, he uses Hye-ryeong as a shield and also kidnaps Yang-sun who is dear to Sung-ryeol.
