CK5 is Crystal Kay's sixth album and first "best of..." album. This album celebrated Crystal Kay's five years in the music business, hence the name CK5, and includes songs on her previous albums, C.L.L. Crystal Lover Light, 637 -always and forever-, almost seventeen, and 4 Real. Since its release, CK5 ranked #2 in Japan's Oricon charts and charted for 49 weeks. The CD's first song, Motherland, was used as the third ending theme for the Full Metal Alchemist anime.

First press edition is 「CD+DVD」．DVD includes 2 LIVE VIDEOS．

This album was COPY CONTROL CD.But changed into CDDA album from July 2005.

CD Track Listing

1. Motherland
2. Eternal Memories
3. Ex-Boyfriend (featuring VERBAL from m-flo
4. 月のない夜　道のない場所 (Tsuki no Nai Yoru, Michi no Nai Basho) [A Moonless Night, A Roadless Place]
5. LOST CHILD [ORIGINAL VERSION]
6. think of U
7. Hard to Say (featuring SPHERE of INFLUENCE and SORA 3000)
8. I LIKE IT (featuring m-flo
9. OVER THE RAINBOW
10. lead me to the end
11. Can't be Stopped
12. 片想い Kataomoi [Unrequited Love]
13. Boyfriend -part II-

DVD Track Listing(First press only)

1. LIVE CLIP（Eternal Memories～CURIOUS）