Once you defeat Spoiler:the Supreme Titan on Easy and Normal difficulties, the game's final boss Spoiler:"The End" will end up being defeated automatically in the final cutscene. However if you defeat Spoiler:the Supreme Titan on Hard difficulty, you will actually have a boss fight with Spoiler:The End before it's defeated in the cutscene.

Both endings are essentially the same except for said boss fight, and the ending song either being "Vandalize" by ONE OK ROCK on Easy or Normal, or "One Way Dream" by Nathan Sharp on Hard.