Replica

From Bliss:
While trying to find a job, Manji, a for-hire bodyguard, also known as “Akainu (Red Dog)”, meets Karu who works for “CARDS”. Discovering that Karu’s mission is to exterminate the deadly “TOYs”, which mindlessly attack any living things, Manji can’t help but forcefully tag along to relieve his boredom…
Edit: Officially a Shoujo manga, though the artwork and action seems to differ.