I Became A Ghost In A Horror Game.

Han Yoo-hee, an unlucky man, finds himself trapped in the horror game [Mystery Exploration Club ~Summer Vacation Nightmare~], where he has become the tutorial boss, a ghost inhabiting a little girl's body named Ella.

Desperate to reclaim his original body and return home, he decides to subtly guide the game's actual protagonists and their group through the treacherous challenges. As he navigates the perilous world, confronting various terrifying monsters, he seeks to uncover the truth behind his predicament and achieve the game's ending.