Beruhren Corporation has developed a new technology "Body Function Expansion Technology" during the war.
People, who used this technology and changed one part of their bodies or the entire body, are called "Extendeds."
Inui Juzo is one of the "Resolvers", who solve problems that arise in a society where Extendeds and non-extended people live together.

Being an Extended himself, Juzo has a giant gun for a head.

One day, Juzo is asked to protect a boy by a fully extended man.
The boy's name is Arahabaki Tetsuro. He was kidnapped from Beruhren Corporation.
However, although Juzo accepted this request, Tetsuro was captured by the pursuers from Beruheren Corporation.
Juzo starts a fight with Beruhren Corporation, company, which controls the entire city...

Who is thefully extended man who kidnapped Tetsuro?
What kind of relationship does Tetsuro have with Beruheren Corporation?