The first version of "Idea" is the full-length version of the song, and not the edit that was used for the opening song of Noein: To Your Other Self. The TV edit of "Idea" appears on the second Noein: To Your Other Self soundtrack CD that was released in Japan, instead of this full-length version. There is also an instrumental version of the full-length version of "Idea" included on the CD single. This instrumental is actually rather nice, because the music is able to stand on its own without having the vocals layered on top of it. If you know enough Japanese to be able to sing along with "Idea," then you could also use the instrumental version to perform a karaoke version of the song.
"Eidos" is a much slower tempo song than "Idea" is. That doesn't mean it's a bad song, however, because "Eidos" is enjoyable to listen to. But the instrumental version of "Eidos" can be hard to listen to. "Eidos" is rather repetitive musically; without having the vocals layered on top to diminish the focus on the music, the repetitive nature of the instrumental is much more noticeable. Again, if you have enough familiarity with Japanese and with this song, the instrumental could be used to perform a karaoke version of "Eidos."
The single for "Idea" is not available for purchase in the United States. In order to obtain a copy of it, you will have to find a retailer who can import it from Japan for you. Your best bet would be to go through an online retailer that specializes in importing music from Japan. If you like the opening song for Noein: To Your Other Self, then I would highly recommend importing this CD single in order to acquire the full-length version of the song. While the TV edit isn't bad, I think the full-length version of "Idea" is a stronger track. For fans of Noein: To Your Other Self, this would be a good addition to an anime music CD library.
I wrote this review after listening to a copy of this CD that my husband purchased for me as a gift.
Idea [Off Vocal]
Eidos [Off Vocal]