I Killed the Player of the Academy

One day, I was reincarnated the world of a game of Heroic Legend of Arhan as Corin Loch, a minor NPC, and joined hands with the game's protagonist, Park Si-ho, to save the world.

However, as the story shifted, I accidentally found out his true nature - a murderous pervert who only wanted to accumulate experience points by hook or by crook! In order to save world peace, I killed him... and became the main character instead of him!

What should I do in the future to bring the game to a perfect ending?