Humans, and the mysterious enemy who resembles them--collectively termed "Non-Humans".
In the midst of this racial dispute, this is a story of various people who pursue their own objectives--writhing in agony, opposing fate.

A heavy collar fixed to her neck, a robotic shackle that counts down to her freedom.
Himena, released from countless days of prison to be reborn as a murderer.
These were the words that were burned into her consciousness at the prison "Hate Breed":

"These are the Non-Humans. Your enemy, the enemy of humanity. Kill, kill, and kill some more. That's your sole path to freedom."

Slaves allowed to live only as long as they continue killing: the FR Slayers.
A robotic counter on the collar increased with each enemy terminated.
To survive, their only choice was to put their lives on the line, again and again.

In the midst of this, a new mission was given to FR Slayer Himena.
Long neglected, a no man's land that no one dared approach: the abandoned island Rumon. There hid an influential Non-Human.
To score kills and raise her counter, Himena enthusiastically set out to Rumon Island. Yet this turned out to be a strategically vital region, so important that the elite squad "Saints" had been dispatched.

Just who are the Non-Humans? And which side will prevail in the end?
Humans and those who defy them--a survival game staking the fate of their species begins.

[From a post on the MangaGamer forums]