Magical Explorer, Vol. 1 (manga)

Reincarnated as a character in the legendary erotic game, "Magical Explorer," it doesn't take long for our hero to discover that he's been designated the unlucky side-character rather than the game's lady-killer protagonist. Not to worry, though! Armed with his vast knowledge of the game (and a few cheats) he'll do whatever it takes to win the hearts of the game's heroines and emerge as the most accomplished student at the Sorcerer's Academy!