Also, this technique can help a bit. To do it, you have to kill all the archers before your grunts all die. Keep a water type swordswman alive. Then at the end, when the boss comes to rape you, you can place Derihourai to the southwest, where's there's only one opening, and let him be hit by the water guy for about 30 damage/turn. The water grunt will block the boss, and give you some time to bring Hakuoro's team.