[NEW MERCENARIES] Please note that all new forum users have to be approved before posting. This process can take up to 24 hours, and we appreciate your patience.
Song is pretty bad for how impactful this boss fight...
In short (without any spoilers), based on your actions throughout the game, you get forced into three separate endings. Chaotic Evil (man on the left), Lawful Evil (man on the right), or Neutral Good (man in the middle, the main character). In the Chaotic and Lawful paths you are forced into this boss fight, and it really kinda forces you to question your commitment to the path you chose.
Overall SMT4 is a great game, but I'd skip it and play SMT4-apocalypse edition instead, since they fix a lot of it's flaws.