Since the CTF was based around greek mythology, I guessed that it had something to do with a greek god.A quick search gives the result of Aphrodite, who was conceived at the sea from Uranus's castrated testicles.
Since the flag format was nicc{daughter_father}, I first tried nicc{Aphrodite_Uranus}. However, it wasn't accepted.
Reading the hint, it says "There are many different spellings, but only one right answer. So try 'em all."
The correct flag ended up being nicc{Aphrodite_Ouranos}, with ouranos being an alternate name for uranus. 