The Guide of Another World

One day, Theodore found a game application that installed itself on his cellphone. A game called Isekai Guide. In the game, it is stated that the main character is a woman who transmigrated from earth to another world named Etheria. Thodore's task in the game is to guide the main character, Rosalina, to kill the Demon King. So that Rosalina can return to her original world. But... Theodore didn't know, that the characters in the game might not be just game characters or npc. And Rosalina, might really be a victim of his world trapped in Etheria. If Theodore knew this, what would he do?