There's a lot going on in this MV.
The Marine who boards the ship has her eye color flipped (including the eyepatch), but the ghost doesn't. My guess is that this Marine is an illusion or reflection created by the ghost, who, after many years, has ended up forgetting her past and identity due to the curse of the treasure box.
At first, the ghost is unemotional, cold, and acts out of character, but she starts smiling in the middle of her fight with Marine. She probably saw her own greed in action, and this triggered something inside her, giving her back a little of her old self.
After her defeat, you can see the dagger with the weird symbols flying to her hand and waking her up. That was probably the curse taking hold of her and controlling her directly to protect the treasure from Marine.
When Marine opens the treasure box, it gives back the ghost's lost memories, and the two of them realize what's really happening. The ghost goes berserk when she remembers that everyone has died, she has lost everything she held dear and she is now alone, so she tries to destroy Marine with all her power because she blames her own greed for what happened.
In the end, Marine realizes that she is the greatest treasure of all, so she destroys the treasure box and frees herself from its curse, allowing the ghost to finally move on.
And there's also this message
>>81839152All in all, it's a fantastic and beautiful story. What a brilliant MV.
