The story/ending is very confusing, at least to me. This narutoforums review shares my own opinion:
The most confusing thing is the picture that the main character's aunt has of the man she is in love with. It looks the same as Chiaki. Is this Chiaki?
Are there any other details I may have missed about the movie or from the book that details this further?
It might very well be Chiaki.
The manga starts with Makoto Konno discovering a young Kazuko Yoshiyama unconscious after having just said farewell to Kazuo Fukamachi.
If the young Chiaki and young Kazuko (the aunt) existed in the same "time stream", the photo might be of both of them.
Also, the picture seems to have a surprising effect on Chiaki, and I can't say who else it might be on that photo. (Doesn't resemble any other characters in the story)
Also, in the movie version, it IS her... It might be a mistake, but that is as close to the fact as one can get, in my opinion.
