The song that Black Maria sang in chapter 992 is of two lovers who longed for each other in a snowy night and they finally met under moonlight.
Here is my theory: the two people mentioned in the song could be Joy Boy and Poseidon (not the present ones but the ones from Void Century).
- The Sea Kings were waiting for a king from distant island (JoyBoy) and Poseidon to meet (as shown during Oden’s flashback).
- JoyBoy made a promise to Poseidon but couldn’t fulfil it. He left her an apology.
- The concept of “Dawn” and “Moon” has been shown to have some kind of relation to Void Century again and again.
- There is something about snow and moon that hasn’t been revealed. BlackBeard’s younger self was shown crying under moon and snow in one of Oda’s drawing (Not saying Blackbeard is related to JoyBoy/Poseidon but to show the correlation of snow and moon).
If we put all this together, the song could be about Joy Boy and Poseidon. The original Joy Boy and Poseidon could’ve been lovers and died without getting to meet each other.
Why were they not able to meet? I don’t know, may be time will tell.
*Theory by AnxiousBottle