In the year 2075, after many efforts, humanity managed to create its first interdimensional portal. Since then and for the twenty following years many worlds, until then inaccessible, have been visited by exploration teams under the control of the UN. They brought back knowledge and technology. Visited planets have been classed into three categories: Earths, similar to our world in many aspects; peaceful Paradises; and the dangerous Purgatories where violence and evil reign.

But, like every door, interdimensional portals work both ways and Purgatories inhabitants began to take interest in it. One world known as “Alcion” saw in the portal an occasion to expand its power, not only on Earth, but also on the many planets now connected to our world. UN security team managed to contain the Alcion threat thanks to its tactics and brutal firepower. So much so that it was soon known to the media and the general public as the “OverKill Unit”.

Less than a month after the victory other purgatory worlds began attacking portals and it’s now up to the OverKill Unit to protect Earths and peaceful paradises.

As a member of the OverKill Unit you are to be sent to worlds where lifeforms and universal laws are very different from what you have experienced so far. Your only mission is to protect each world’s portal against the assault of its residents until the command center brings you home and deactivates it. If you fail, the command center will fall in the hands of hostile creatures which could then ravage your home, and many more.