This is the first achievement in the game. Just progress through the school to find yourself in Yokohoma city. There you will need to aquire a golem to enter the golem arena. For this you need some golem tickets, one from the Pizza vendor and others from around the area. After you have gotten into the golem arena, win the first fight to come up against Yuki. Survive for as long as you can, as midway through the fight a disaster will happen and you will find yourself outside in a ruined Yokohoma city. There you should get the achievment.