Limited Edition w/ DVD cover
- This single comes with a Limited Edition w/ DVD version, or the regular CD Only version. In this case, the versions have different covers (as seen above).
- In this single's credits, Yamato lists himself as "Helicopter Kid Yamato"; Naoto lists himself as "programming, other instruments, g."
- "O2" was used as the opening theme to the TV anime Code Geass: Lelouch of the Rebellion R2, the first anime song Orange Range has done since "*~Asterisk~". A series of CMs were produced featuring Orange Range and the Code Geass main protagonist "Zero" to promote the OP. The anime version is a different recording from the album version.
- "O2" is the first single in which Yamato takes the lead vocals (as opposed to Hiroki).
- The PV for "O2" was recorded at Toei-Kyoto Studio Park; the PV features a parody of an old Japanese love tale between a samurai and a princess; each of the band members had a role in the story (Hiroki as a Sri Guru, Yoh as a Umbrella Craftsman, Yamato as a Wind-Chime Craftsman, Naoto as a Kokeshi Craftsman, and Ryo as a Soba maker), and towards the end of the song the band gets together and battles samurai. The samurai and the princess were played by Satou Sakura and Emoto Tazu respectively.
- "Harujion" is a Okinawan "reggae" style song that is slow and gives off a tropical vibe. The screeching voice at the end is Hiroki, by the way.
- "Sekai World Uchinaanchu Kikou (DJ TASAKA REMIX)" is the longest song released in Orange Range's history at a sizable eight minutes and ten seconds. The song is a remix of "Sekai World Uchinaanchu Kikou", which is released on the album PANIC FANCY (that song is only ~3 minutes).