Karyū

was the head of the Dark Thunder Group.

Background
Karyū came from a small village in the Land of Lightning. Since the members of his clan owned a kekkei genkai, Kumogakure often employed them during its battles. Seeing that he was eventually going to die as a tool, Karyū decided to leave his village and become a missing-nin.

As he was about to being captured by Kumogakure's hunter-nin, Karyū was found by the head of the Lightning Group, a kekkei genkai user like him, who accepted him in his group. Karyū began taking part in the Lightning Group's activities, such as robbing the rich and redistributing the plundered money to the poor villages.

When the Lightning Group disbanded after being lured into a trap by Kirigakure, Karyū began living as a fugitive again, cursing the villages that refused to help him in fear of the shinobi villages' possible retaliations. After many years in hiding, Karyū came to know about Sasuke Uchiha's attack at the Five Kage Summit: being impressed by the fact that Sasuke, a kekkei genkai user, wasn't afraid of opposing the shinobi villages, he decided to start gathering people for his revenge against the villages that denied him refuge, calling his old comrades back and forming the Dark Thunder Group.

After the Fourth Shinobi World War, the Dark Thunder Group began growing in size because of the recruitment of unemployed shinobi. Then, Karyū began carrying out his revenge, sacking the villages and killing all their inhabitants.

In the anime, however, Karyū was a kekkei genkai shinobi who worked in the guard unit of En Oyashiro. He escaped with Fūshin, Chino, and two others from En and they formed the Lightning Group after helping the Bamboo Village by stealing money to give to the poor villagers. After being betrayed by Kirigakure and the villages they'd helped, Karyū left the group and lived as a recluse.

Personality
Karyū is described as a vengeful, cruel person, not showing mercy towards the people who weren't directly involved in his downfall. Sasuke notes that he resembles his old self.

Karyū also showed an obsession towards Sasuke, idolising him as his "master", though he also wished to surpass him by killing him. In the anime, Karyū is seen as a bit of a coward, as he was afraid of Sasuke after their fight.

Appearance
Karyū has long bluish-purple hair (red in the aniime), and anaemic-looking lips.

Abilities
Using Lava Release, Karyū was capable of creating black vulcanised rubber-like material, that took the form of balls and liquid, which he could use in conjunction with walls of earth.

Sasuke Shinden: Book of Sunrise
As the head of the Dark Thunder Group, Karyū had been destroying many villages around the Land of Hot Water, the Land of Water and the Land of Lightning, including the village in which Iō's daughter lived. When he planned to destroy the Bamboo Village, he came to know that Sasuke was there as well, and decided to meet his alleged master.

After Sasuke, who had gone to Iō's daughter's village to investigate, was warned by Chino that someone was attacking the Bamboo Village, Karyū was finally able to rendezvous with the man he longed for. The two engaged in a battle, resulting in Karyū's loss despite he made use of his strongest techniques.

Upon being captured and restrained with the rest of the Dark Thunder Group, Karyū revealed Sasuke his past and the reason of his grudge towards the village. However, before Sasuke could interrogate him further, Karyū perishes in a fire that involved the whole Dark Thunder Group as well as Iō.

Anime
In the anime version, however, Karyū is hired by Fūshin to impersonate him and implicate himself in the exploding humans in order to draw Sasuke for Chino and Fūshin to kill him. He is blamed by the Bamboo villagers for the exploding humans and then appears at the Coliseum long enough for Sasuke to chase after him. When they arrive at the Land of Hot Water, Karyū and Sasuke fight but Sasuke easily defeats him and threatens to kill him. Karyū surrenders and Sasuke sees through his memories with his Sharingan, discovering the truth. Karyū runs away when Fūshin appears to confront Sasuke. After Chino and Fūshin surrender to Sasuke, they and Karyū are sent to jail but are offered to work for the Mizukage as part of Kirigakure's atonement for betraying them, and all three accept.

Trivia

 * When written as "加硫", Karyū's name means "vulcanisation"; a reference to his kekkei genkai.