Yuuka Shinchiro is a 2nd year highschool student whose parents passed away several years ago in an accident.
When he's walking through a park at night, a child's head jumps into his hands and he's bitten by an alien. Soon after, he wakes up and dismisses what happened as just part of his dream. When he wakes up, the bite mark is appears just where it was in his "dream"!
The next morning, the news reports that a child's head is found in a park along with lots of blood. As he goes to check out the scene, he finds a violent man asking him about the "abyss". The violent man later visits his house and calls him the Grim Reaper.