This used to be one of my favourite movies and I still like it upon rewatching it recently (but in Japanese this time) but I don't love it as much as I used to. My favourite thing about this movie is the setting with all the canals and water. I also love the music, especially the Latias theme.
The person who kissed Ash at the end could be either Bianca or Latias. The reasons are below:
- had more contact and interaction with Ash throughout the movie
- didn't wear a hat
- didn't talk or even breathe
- left her hat behind
- had an interest in painting (could've drawn it for Latias)
- didn't talk because she didn't want Ash to know it was her
- has a secret crush on Ash
I think the writers left it open to our own interpretations.