Set in 2100, it has now been a century since humanity has been hounded by creatures one could only describe as genocidal demons,thirsting for human blood and destruction.

Against humanities best efforts to keep these creatures at bay many towns were eradicated within hours and at best days, in the present day only a handful of towns were able to survive, even if barely.

Amongst those towns was a city called Mono Town, short for Saigo no mono, meaning "The last One" as it is, as the name suggests, the last city built around and on structures that existed pre-bloodshed.

Even with massive concrete walls with steel skeletons and many heavily equipped soldiers standing on top of them, the monsters still manage to slip through into the town and terrorise the locals, for that the city trained and deployed undercover assassins to take care of these vermins.

Why undercover? If any news or rumours about these monsters penetrating the cities guards and walls came to light, mass panic would un-roll within hours.

Years later after implementing these assassins,they became scarce as the monsters eventually outnumbered them. But one faithful night a stranger appeared in this city, they were swift as a cheetah, strong like a tiger, quiet as a black-footed cat and intimidating as a lion. Being able to take down gangs of these vermins within minutes, they were respected amongst assassins and city folks.

No one to this day knows who this mysterious saviour is, many even speculate it may be multiple people running this operation.

Will the city get to know who this killing machine is or will they continue undercover? Why must they hide anyway? Are they hiding some dark secret they simply can't let the city know?