From * Mangahelper *:

Humanity is on the brink of extinction as a flower known as “Viscar” infects humans and animals, turning them into mindless hosts that feed on others. If you get bitten by the infected, or inhale the pollen that emits from their bodies, the flower will plant itself into your brain. Humanity is fighting a losing battle against this world-wide pandemic, and most people have given up hope.

Volt was once part of the army and had been assigned to be the guard of Dr. Kisling, the scientist leading the development of a vaccine to fight against the Viscar. From an unfortunate accident, one of the contained Viscar pollen escaped, infecting Dr. Kisling. Dr. Kisling’s final wish to Volt was to find his daughter Lilith, and, with her help, continue the development of the vaccine. Lilith and Volt now venture into the post-apocalyptic world to bring back hope to humanity.