Hidden Ending Saengseong Jungimnida

The day after seeing the ending of the game 'Return of the D-Class Hunter', Yeon Seon-Woo, who has been possessed by an extra in the game, is kidnapped by the main character 'Lee Je-Hee'. Lee Je-Hee, who has been suffering from insomnia, proposes a contract, saying that he needs Yeon Seon- Woo as a mentalist, and he is semi-forced into signing the contract.
[Listen to your master's words and become a beloved servant!]
"...A beloved servant? Master? What do you mean?!"
Isn't this a 'slave contract'?! In order to return to the real world, he must find the hidden ending. Will Yeon Seon-Woo be able to escape the game?
(Source: Ridibooks)