Or either way around the ncp to attack on the main character (instead of a monster).
Are you using a special battle system or just DBS? Because you can get an event to follow a hero and then call a battle on Event touch. Then dispose of the event once the battle is over. To get the PC to attack an NPC, you can use a parallel process common event, and if the player is facing an NPC and pressing a certain button then you can call a battle. But you need to be more specific?