In an imaginary age of gods about 20 years after the war, Japan is flooded with all the superhumans ever written about in fictional stories: titans from outer space, lifeforms from a mystical world, phantoms and goblins from ancient times, cyborgs created by scientists, relics that rose out of the ruins of ancient civilizations, and the list goes on. Some of them make no secret of their existence and have gained popularity in the society, while others cloak their identities and fight in secrecy.
Naturally, the Japanese government cannot ignore the existence of these superhumans and establishes an organization under the Ministry of Health and Welfare - the Overpopulation Research Laboratory, a.k.a. the Superhuman Bureau. Their mission is to identify and approach superhumans, then oversee and safeguard them.

"UN-GO" is a full-fledged detective story about a detective and handsome boy combo who tackle the world's most difficult crimes together for reasons of their own.

The profession of private detective fell out of favor long ago, and yet, that's how the young man, Shinjurou Yuuki identifies himself. With his superior deductive powers, Shinjurou solves various challenging cases. Meanwhile, Inga, an attractive young lad, serves as Shinjurou's "buddy". But contrary to his cute looks, he's a sharp, arrogant rogue. Why Inga sticks with Shinjurou is as yet unknown.

The setting of the story is a postwar, future Tokyo that still bears the scars of war. Ruling the land is Media King Rinroku Kaishou, who through politics and industry has the communications infrastructure under his thumb. Kaishou has used a clear head and the massive amount of information at his fingertips to lead to the solution of a great number of cases.

But there's an underside to Kaishou's brilliant deduction work, which is that Shinjurou Yuuki, "the Last Great Detective", is the one who actually uncovered "the truth" in those cases. However, the public doesn't know this and thus refers to Shinjurou as the "Defeated Detective". Still, Shinjurou, together with Inga, can't help but search for the truth.

From MangaHelpers:

During the feudal era, warlords were not only in danger from enemies outside the castle, but also from within like their own lieutenants they trusted. To protect themselves, they secretly began to use decoys of themselves. Honda Masanobu was part of Tokugawa Ieyasu’s council and also his closest friend. However, to defend his home country from Oda Nobunaga’s campaign, he leaves his position. During the 10 years on the battlefield, he meets Jirosaburo Motonobu who looks almost identical to his former master. Masanobu comes to realize that Jirosaburo must become Ieyasu’s shadow because of his trustworthy character and battle experience. [vyc]