What does it mean?
It means several things, but there is one meaning in particular that you need to understand.
For the better or for the worse I still don't know.
But Chatnoir is no longer in me anymore.
I'm Chatblanc now.
And the time for betrayal is now here.
Once upon a time, Chat Noir and Ladybug saved their city together. Once, they worked as a team, and loved each other dearly, whether it be as partners or as lovers. Once, they knew that they could trust each other with all their heart.
But, that was once. Once upon a time, far back before all of this happened. Before the betrayal, anger and sadness took place.
With Chat Noir akumatised, Ladybug suddenly begins to start questioning everything about her life, and begins to wonder whether or not she can really shoulder the burden of rescuing Paris on her own.
Especially when her partner is trying to rip her throat out.