Kokoro no Tamago
- Kokoro no Tamago (こころのたまご; The Heart's Egg)
- Kawakami Natsuki
- Muramatsu Tetsuya
- Other Information
- Arrangement, Programming, and Keyboards: Abe Jun
- Guitar: Suzuki Kenji
There are currently two versions of "Kokoro no Tamago" to be found in Buono! and Hello! Project's discography. These versions are:
- Kokoro no Tamago (Original)
- Found on the "Honto no Jibun" single as track #2, the Café Buono! album as track #9, the Shugo Chara! Song♪Best album as track #12, and the limited edition Disc 2 of the The Best Buono! album as track #1.
- Kokoro no Tamago (Instrumental)
- Found on the "Honto no Jibun" single as track #4. This is the standard version without the main vocals.
-  Buono! Kessei 1 Shuunen Kinen FC Special Live ~Rock'n Buono!~
-  Buono! Live 2009 Hybrid★Punch
-  Buono! Live Tour 2010 ~Rock'n Buono! 3~
-  Buono! Live 2012 "R.E.A.L"
-  Buono! Live 2017 ~Pienezza!~ (as part of a medley)
- projecthello.com: "Kokoro no Tamago" lyrics