18+ Magical★Explorer: Eroge no Yuujin-Chara ni Tensei shita kedo, Game Chishiki Tsukatte Jiyuu ni Ikiru

The legendary game full of pretty girls: Magical Explorer! Getting transported into your favorite harem romance game is the dream, right? But when one poor guy is cast as the main character's BEST FRIEND, it's more of a living nightmare! After all, living as Kousuke Takioto means watching his best friend win over all the girls—and getting none for himself. That's how the script goes, anyway. But if he uses his full knowledge of the game to his advantage, maybe there's still a chance! A chance to turn his nightmare into his own private paradise...

(Source: Yen Press)