In The Parallel World  (English, Paperback, Umang)

"Ichiro Suzuki is a 29-year old game programmer who was tasked with fixing several bugs in two MMORPGs his company is preparing for publication. However, he becomes extremely worn out as he is working during the weekend. After taking a nap, he mysteriously wakes up in a parallel world that resembles some of the fantasy RPG worlds he had worked on, as a 15-year old named Satou, later Satou Pendragon, a nickname he uses while running beta tests, and with what looks like the menu screen of the game he was working on appearing before his inner eye. However, before he can grasp his current situation, an army of lizardmen ambushes him and launches an all-out attack on him. In desperation, he uses all three of his special 'Meteor Rain' attack options."