Once the protagonist Chocobo, Boco, reaches level 100 and has encountered Koko, the love interest, the Demon King will capture her, forcing Boko to chase after him to save her. The demon has 99 HP, but is quite slow in attacking. Upon his defeat, the player will have fully completed both scenarios of the game.
A trick to easily encounter the demon is to set the "move" selection of the game to 1; then every battle will be with the final boss.
demon is "an evil spirit or devil, especially one thought to possess a person or act as a tormentor in hell."A