AD 2006, Mankind encounters a mysterious Phenomenon called "Algernon". Nothing is known about Algernon, all people involved with Algernon are dead. One day, the mysterious phenomenon Algernon happened at an underground Amusement park where our hero Keita met our heroine Hinoki, driving "Kakuseijin". Keita and Hinoki encounter a lot of mysteries and monsters. What is "Algernon"? And what is "Better man"? Why does Better man help when Hinoki and Keita are in danger? The never ending nightmare has started.
Keita Aono goes to school one day, and his class happens to have a new student. That student is a girl named Hinoki Sai, Keita's childhood friend. Later, Keita gets himself lost in an amusement park where many people have mysteriously died. Keita catches up with Hinoki, and the two are attacked by a large monster. Who will save them? The being known as Betterman.
Keita learns more about the Akamatsu Corporation and the mysterious figure Betterman.
Keita, Hinoki, and Asami fly overseas, but everyone else on the plane mysteriously disappear. Keita and the gang get attacked by possessed crash test dummies.