Sometimes having three girlfriends is better than one, unless they share the same body. 

The mighty Labda, Cilla, and Katina are three heads, sharing one hellhound body in an anthropomorphic form. In the underworld, they are the guardians of the gateway between the living and dead, until a monster outbreak occurs, led by the evil Medusa. The three-headed Cerberus girl must hunt the other monsters thrust into the human world or face their own destruction. 

Meanwhile, Roger Bullet is a tough cop who always fights for justice. When a snake girl murders his partner, Labda, Cilla, and Katina rescues him from the same fate. For saving his life, Roger helps the Cerberus while a romantic relationship builds up between them. How awesome could Roger's adventure get?

P.S, my word count will be between 500 to 2,000 words in each chapter.