Extra Existence (エクストラ・イグジステンス) is a manga series by Etorouji Shiono. It was serialized in Comic Gum.
13 years ago, an unknown object appeared at Shinjuku. That creature will give birth to a devil creature regularly. Therefore, our world is being eaten clean. The military found a weapon capable of fighting these creatures, a special power known as "exex" that becomes part of the human body.