(from ebookjapan):

The word "Mezzon," meaning "middle child," has been turned into the name of an organization that stands in the middle of the world's two major powers and protects peace - and it has become the name of an organization that protects peace. Kenji, a curious boy, saves his brother, Mezzon J, a member of the Japanese branch of Mezzon, from a difficult situation and becomes a member of Mezzon.

Mezzon Z" was born! Just as Kenji becomes accustomed to handling the Mezzon uniform with its various secret weapons, his older brother, Mezzon J, goes missing. In order to rescue him, Mezzon Z heads to the "Island of Superhuman Brains," but...?

A near-future spy action manga!