In Another World With My Smartphone: Volume 1 by Patora Fuyuhara

After a freak accident involving some lightning winds up zapping him dead, 15-year-old Mochizuki Touya wakes up to find himself face-to-face with God. “I am afraid to say that I have made a bit of a blunder...” laments the old coot. But all is not lost! God says that he can reincarnate Touya into a world of fantasy, and as a bonus, he gets to bring his smartphone along with! So begins Touya's adventure in a new, anachronistic pseudo-medieval world. Friends! Laughs! Tears! Inexplicable Deus ex Machina! He sets off on a journey full of wonder as he absentmindedly travels from place to place, following whatever goal catches his fancy. The curtains lift on an epic tale of swords, sorcery, and smartphone apps!