I'm...in... LOVE with this animation!!! Oh my god, what a cute and lovely story! ;D
I like the length of this, didn't feel like an eternity but was long enough to really let the viewer dive into this story. It has those constant changes between happy moments together -> sad and depressing moments.. Those perspective changes where we viewed everything from the character's eyes and where everything was 3D were also a nice touch.
It's just generally very touching how far they went to cure that seemingly incurable disease. After all the struggles, mutations... they still embrace and love each other ^_^ I can really see that you've put your HEARTS into it... heheh :D
Fantastic job, please keep more awesome stuff like this coming ;-;