No, it’s not the official image album nor the OST. This is just a doujin image album by Voltage of Imagination which started way back 2008 at the C74 up to C76 in 2009. The author himself is not involved in it too. Anyway, there are 4 albums: GET SET, AHEAD, BREAK and GO AHEAD. onoken provided the music while Chata, Aki Misawa and Rekka Katakiri provided the vocals.
It’s English title is “The Ending Chronicle“. It’s a light novel written by Minoru Kawakami and it’s illustrated by Satoyasu. Actually, there is NO English translation of this. But I’ve heard that there’s a drama CD version of it. And so far, no manga and anime version of it yet.
The story is set in an alternative timeline in Japan dubbed as Republic of Greater East Asia. One class of high school students went on a field trip until they were put to sleep and later, woke up in a “classroom” with metal collars around their necks.
They realize that they have been selected in “The Program” (aka Battle Royale Act) in which they are forced to kill each other in the island until one survives. The collar placed around their necks has a bomb in it and if anyone attempts to remove it or enter the forbidden zone, the collar will explode.