Sometime in the future, somewhere in Europe, a city has many levels of underground, secret, dangerous levels that have answers to the past. Mihai is a retired assassin who has returned home to settle a vendetta and start a new life as a restaurant owner. Haine was genetically experimented on as a child, which led to him possesing dog like attributes. Badou is his clumsy chain smoking partner who becomes deranged when denied cigarettes. Naoto was orphaned as a child and has amnesia was trained to wield the sword. Their pasts are somehow connected to the secret underground and the organization that controls it.