Looking for animation about a little girl and a boy who can shapeshift into a shark

Question

I first watched this animation on Youtube several years ago; 4-5 is my best guess.

What I remember:

• The girl wore yellow and had either blue hair or eyes; or both
• The boy was an assailant trying to kill the girl
• On a ship, later an island, and then a ship again
• Vibrant colors
• Something really sad. I cried hysterically, I don't remember why. This is also the main reason why I am trying to find this animation
• I remember the boy could shift into a shark
• The girl was somewhere between 3-6 years old, and the boy was more teenager

Is there an animation that fits this description?

Edit: I think the boy's name was some color. I don't remember which color though.