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.