Re-Zero Vol. 1 (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?