Rezero Starting Life In Another World Vol 1 Light Novel

Subaru Natsuki was just trying to get to the convenience store but wound up summoned to another world. He encounters the usual things--life-threatening situations, silver haired beauties, cat fairies--you know, normal stuff. All that would be bad enough, but he's also gained the most inconvenient magical ability of all--time travel, but he's got to die to use it. How do you repay someone who saved your life when all you can do is die?