Okay, I've tried listening to all the tracks on this site:
http://fish.kakiko.com/toutsukai/
And the ones with very strong similarities to me are:
- Smily (vocals and melody)*
- Kingyo Hanabi (melody, rearranged)
- Neko ni Fuusen (vocals)
- Ishikawa Osaka Yuukoujouyaku (melody) - but isn't this more of a cover? Ai Otsuka does include the original song as a background.
- Planetarium compared to Shiawase ni Kumo no Ue ni - second to the last in the Ai Otsuka section (vocals)
- Will (melody of the Kiki's Delivery Service track becomes the vocal style in Ayu's song)
- Sakuranbo:
http://pya.cc/pyaimg/pimg.php?%20imgid=3561
I'm very sure that Smily is not accidental. It's the only one I can't dispute. It's too much of a coincidence. Vocals, even the musical notation is the same! I even tried it on the piano.
This makes me very sad
But what's really surprising is that two Joe Hisaishi tracks are mentioned! (Kingyo Hanabi is from My Neighbor Totoro and Will is from Kiki's Delivery Service). Well, at least Ai and Ayu have very good taste.
Of course, maybe someone around here could prove me wrong?
Edit: I still wonder why the Koda Kumi youtube video is off limits? There wasn't anything risque. Are fans responsible?