Jiro Azuma

Jiro Azuma (我妻 弍郎, Azuma Jirō) is a ninja who can talk to animals. His grandfather trained him in martial arts since his childhood. He joined the Bureau of Espionage after he fused with Rago, a mononoke.

Plot
Jiro Azuma, a ninja who can talk to animals and was raised by his grandfather, meets a mononoke named Rago. Mononoke are immortal demons with extraordinary, supernatural powers. Rago is badly injured and Jiro, who has a soft spot for the animals he can talk to, treats Rago's wounds. Another mononoke attacks Rago and Jiro dies protecting him. Rago returns the favor by fusing with Jiro, bringing him back from death but forever changing his life. This fusion gives Jiro the power to crush his opponents with Rago's power, but in exchange, he is no longer human.

Immediately after defeating the evil mononoke, Jiro is detained by Ryosuke Shiba and Ichika Kishimojin, goverment employed ninja from Bureau of Espionage. The Bureau was pursuing Rago after he was freed by a mysterious group of mononoke during a raid on the Bureau. Jiro, no longer considered human by the Bureau due to his irreversible bond with Rago, is forcibly put under surveillance and protection, effectively becoming their prisoner.

Jiro managed to escape from the Bureau to return home to his grandfather only to learn that his grandfather is a former member of the Bureau! After a bitter fight, Jiro decides to return to the Bureau on his own to fight against the mononoke and humans who now want to use him. However, on his way back, Jiro and his escort, Ichika, are attacked by mononoke who want to use Rago's power for their own evil ends! Jiro and Ichika manage to defeat the mononoke together.

There’s a new squad at the Bureau of Espionage—code name: Black Torch. The squad, run by Shiba, consists of Jiro, Ichika, Hana and one more rookie named Reiji. However, Reiji refuses to work with a guy who has fused with a demon and almost immediately comes to blows with Jiro!

Their first mission leads them to the place where Rago had been sealed. They successfully fight off the mononoke there, but it leaves them with a cryptic message about Jiro's birth father.

Days later, the squad is brought together for some anti-mononoke training. Forced into an illusion courtesy of the human-friendly mononoke Fuyo, each member of the group confronts their own individual trials. Jiro and Rago, must do battle a colossal black panther, the true form of Rago.

During an anti-mononoke training session, Jiro and Rago are shown a vision of the Edo period. There they meet a mononoke named Amagi and learn he was the one who had Rago unsealed from his prison.

Days later, a string of mysterious murders is revealed to be the work of mononoke, and Black Torch is given the order to act. Sent alone into the haunted town, the three members of Black Torch quickly run across the mononoke responsible and the battle begins!

Jiro and Rago take out Kanawa, but in the process Rago becomes aware of a horrifying truth - in exchange for granting Jiro his powers, he has been unwillingly devouring Jiro's vital energy this entire time! Before Rago can tell this to Jiro, the two are confronted by Amagi himself. Jiro tries to fight, but is crushed in a single blow. In complete control, Amagi delivers an ultimatum to Rago - if he wants to save Jiro's life, he must swear his undying loyalty to Amagi!

With little other choice, Rago allows Amagi to undo the possession binding him to Jiro. However, Rago pulls a fast one on Amagi and leaves all of his power behind in Jiro.

Later Jiro is having problems controlling Rago's power. His grandfather, Toshimasa, comes out of retirement to help him, taking him to the Avidya Forest. With the help of the forest's master, Ibuki, Jiro finally starts getting the hang of Rago's power. After a long training session, Ibuki tells Jiro a little about Amagi and his unique ability to strengthen himself by devouring other mononoke!

Afterwards
Many centuries ago, a mononoke gifted the ancestor of the Azuma Clan with heightened athleticism and the power to speak to animals. All later generations inherited these abilities to a greater or lesser degree, though in Jiro's case they came through particularly strong. His eye-opening physical talent and ability to speak to any animal right away (when it usually requires spending a lot of time together to learn to speak with even a single animal) result from this.

Toshimasa is Jiro's maternal grandfather. Since his mother died shorty after he was born, Jiro was effectively raised by Toshimasa. He has never even met his father.

After the battle with Amagi, the Buerau recognizes Jiro as an official onmitsu agent. They also enroll him in a special high school they directly sponsor, which Reiji and Ichika also attend. Being a high school student and an onmitsu specializing in mononoke cases means Jiro's life grows exponentially busier, but he doesn't seem to mind.

One day, the Bureau acquires information that a certain massive corporation is secretly in league with mononoke, contracting with them for assassinations and dangerous experiments. What first seemed to be a cut-and-dried case of corporate espionage soon turns into a sprawling conspiracy involving assassination of Bureau VIPs, exporting mononoke to foreign countries, replacing powerful politicians with imposters, and more.

The secret war against mononoke grows fiercer. Plots and plans on a level Jiro doesn't truly grasp grow more devious. All Jiro knows is that he's getting perilously close to having too many absences from school. But through all the whirlwind of activity, he starts catching glimpses of his father.

Power & Abilities
Unlimited Power: Rago provides Jiro with power however Rago drains his life energy during the process

Enhanced Strength: Jiro already has the basic skills of a ninja (After being trained by his Grandfather, Toshimasa), having his skills combined with ragos power he is seen as a Country Level Threat. After Jiro learns how to control Rago"s power during his training with Ibuki, he acquires a new form ( Nue 30%). 

Nue 30% : Being a god-yokai, his strength and endurance is immense. Having his endless black aura around him, makes him extremely tough with great defense (Enough to with-take a tank bullet). He can shape his aura the way he wants and thus can create surprise piercing attacks. Gathering aura in his mouth, he can create an energy blast eradicating everything in his path (Similar to Naruto's Tailed Beast Bomb).His real strength comes in when he completely transform into his original form.

Nue 100%: In this form, he gets bigger and his raw strength triples. Most of his body in made out of his endless aura, making him even more tough and formidable enemy.