The end of the game. Aquaticus, Dragon God of Water, kidnaps Micah's fiancee on the day of the wedding. Micah breaks into the Dragon Cave (with Majorie and Ondorus' help), fights to the lowest level, and beats the everloving shit out of a literal god for the sake of his lover. Afterwards, Aquaticus tells him he's proven himself worthy and offers to reveal Micah's past and send him home, and Micah responds by declining, picking up his lover, and marching home. And then after the credits you can go back and beat him up again for shits and giggles.
If you rebattle him while on Shino's specific request for him, or do it in the labyrinth, you'll realize he was pulling a I Am Not Left-Handed and is much, much stronger now, having gained new attacks.
The boss fight itself has one at the end, when Aquaticus tells you he hopes you realize the futility of this before you drown, and your fiance tells you to give up and go before he kills you. Micah's response?
Micah: I won't give up! I will NEVER GIVE UP!
Aquaticus will then launch an attack that basically does a couple hundred points of damage PER SECOND, and Micah KEEPS WALKING THROUGH IT to deliver the final blow.