To understand the ending is to understand the clues the drama has dropped Chaos Pearl, Chaos Power and the last epi.it was stated the Gu butterflies have flown out from the Dark Abyss,signalling a major event going to take place. This drama is like Picasso painting ,to understand certain things for one s to enjoy it in its fullest senses.

Chaos Theory of the Butterfly Effect

“A butterfly flapping its wings in Brazil l can cause a tornado in Texas:"-the Butterfly Effect: If the butterfly had not flapped its wings at just the right point in space/time, the  tornado would not have happened. Chaos Theory describes a slight change in the initial condition could have a vast impact on the outcome, Historical fact- the Nagasaki A bomb dropped instead of  Kokura as it was obscured by cloud cover. A small change changed the course of history.

AZ was the Chaos Pearl,, divine artifact controlling time and space.She createdHigh Divinity Circle/Time Controller /Rebirth, before her death to wait for a Special One.(She had said it will 10,0000 years before she can meet with ZM again.)When XXC travelled to meet High Divinity Circle, the 1^st time, he failed to kill HXW. The 2^nd time.he wanted to bring MXL back to Snow HilL to live a happier life from the Dark Abyss.,This time he succeeded as High Divinity Circle knew he was the Special One. ZM merged with ZM and AZ merged with MXL.(rebirth) Last clue dropped to tie up the ends, where the camera panned down to FL's tiny bells on her footwear in the last scene  of last episode ,reflected from 1^st scene of 1st epi., when FL walked towards ML to kiss him.

Hope you enjoyed the drama as much as I do after making the connections. LOL!!

If you like more connections,read my reviews on psy term "inner demons",. I had said early in  the  comments section that this drama  has lots of psy. terms..  Psy. projections (blame-shifting), delusions, schizophrenia (HXW) etc  It was so much fun trying to pick those up., like  picking  gold nuggets from pebbles!!  Educational and Entertaining! LOL!