Death March kara Hajimaru Isekai Kyousoukyoku

From MangaHelpers: 29-year-old programmer Suzuki Ichirou finds himself transported into a fantasy RPG. Within the game, he's a 15-year-old named Satou. At first he thinks he's dreaming, but his experiences seem very real. Due to his use of a 3-time-use special power (meteor shower), he ends up wiping out an army of lizardmen and becoming very high level. He hides his level and plans to live peacefully and meet new people, though developments in the game story (like the return of a demon king) might get in his way. [tethysdust]