'During the first week, more than 80% of the world's population died. It all started with a plague then it brought death and sorrow, but it also gave us, the survivors, special abilities.
Isaiah wanted to use magic to teleport but that would tire him out later after reaching the kingdom of darkness and he would end up loosing more than half of his magic and it would take a copule of days for him to restore his magic completely so, he just decided to ride a horse.
"Yes, I confirmed it personally. Every morning, he runs ten kilometres, does 100 push-ups, and also, never forgets to perform sit-ups as well as squats, too."