Reincarnated Into a Game as the Hero's Friend: Running the Kingdom Behind the Scenes (Manga) Vol. 1 by Yuki Suzuki

In this isekai fantasy, a modern man is reincarnated into a game world as a doomed background character...who can help save the world as the hero's shadow. And don't miss the original light novels, also from Seven Seas!

For every legendary hero, there’s a loyal best friend. When a Japanese gamer reincarnates into the body of Lord Werner, a faceless mob in the world of a video game, he sets out to make sure the hero Mazel is up to the task. He’ll need to train him, teach him etiquette, and make sure his pockets are overflowing with potions! This is not the story of the battle between Mazel and the Demon Lord. This is the story about one man’s attempt to make sure he doesn’t end up as collateral damage!