The Rain village is located in a poverty-stricken country that, due to it's location, had been the battleground for warring ninja villages. Because of this the village is filled with refugees and orphans. The Rain village is also very secretive, all travelers must state their business and are watched continuously until they leave.
Roughly 30 years ago he encountered Jiraiya, Orochimaru, and Tsunade during the second great ninja war. He knew that the Leaf village would win the war and killing them would mean nothing, so he decided to let them leave. He acknowledged their incredible talents and said that he would honor them as the Leaf village's " Sannin."
Over 10 years later, during the prolonged war between the Leaf, Sand, and Rock villages taking place in the Rain village, an organization sprung up within the Rain village that grew rapidly and battled against all sides. Hanzo came to the organization's leader, Yahiko, saying that he can use them to form treaties with the warring villages. When Yahiko and Nagato showed up to the assigned meeting place they found Hanzo along with Danzo of the Leaf village's Root, learning that they had come to an arrangement; Hanzo would help Danzo become Hokage, and Danzo would help solidify Hanzo's leadership of the Rain village, and getting rid of Yahiko's band of rebels was the only way to accomplish this.
Yahiko and Nagato found that Hanzo had their companion, Konan, hostage and threatened her life if Nagato didn't kill Yahiko. In order to save his friends, Yahiko committed suicide. After this, Hanzo ordered his soldiers to kill Nagato as well. They threw kunais, but Nagato repelled them with Shinra Tensei and leaped after Konan, Hanzo backed away and revealed his trap, Nagato's legs were covered in paper bombs but Nagato remained standing after the blast despite his legs in horrible shape. Nagato then summoned the Heretical Demon Statue, at which point spikes extended from it and pierced Nagato's back which withered him, and an energy came out of the statue's mouth that removed the soul of everyone it hit. Hanzo however was not that easy to hit and retreated.
Many years later, the elderly Hanzo had become a paranoid shut-in, being guarded 24/7 by some of the village's most elite ninja and required all visitors be searched. Eventually a civil war broke out in the Rain village between Pain and Hanzo, with the existing ninjas in the village choosing sides. He was eventually surprised by Pain in his home, whom voiced his disappointment with what Hanzo had become, and took leadership by killing Hanzo. Pain then killed Hanzo's close and extended family and everyone Hanzo ever associated with.
Shinobi World War Arc.
Hanzo has recently been resurrected by Edo Tensei, along with many other powerful ninjas, to fight in Akatsuki's war against the united power of the great nations. He would be sent in a group with Chiyo, Kimimaro, and Chukichi. Together, they attack the alliance's Ambush Squad led by Kankuro. Deidara begs to be let out, but Hanzo refuses to do so, claiming his hatred for the great villages. As they flee, Hanzo summons a salamander which carpets the entire area in poison, stopping the Ambush Squad from escaping. Hanzo went in for the kill, but is stopped by the samurai leader, Mifune.
Chiyo reveals that Hanzo's salamander needs 5 minutes to create more poison, irritating Hanzo. As he and Mifune clash swords, they also clash words. Hanzo questions Mifune's samurai ways for allying with ninjas, but Mifune insists that he's fighting for peace. Hanzo says that he once tried to get the five great villages to unite to achieve peace, but it was an abysmal failure. Mifune then says that Hanzo gave up on his ideals and retreated into his seclusion, and that he won't lose his faith like Hanzo did. Hanzo tries to use ninjutsu, but Mifune stops him. Hanzo realizes from Mifune's moves that he fought him before, Mifune confirms this and says that he survived their encounter.
Hanzo's salamander appeared from beneath Mifune and trapped him in it's mouth full of poison, but Mifune held his breath and cut the salamander in half. The two then charge at each other, but Mifune cuts through Hanzo's weapon and deals a devastating blow. Hanzo questions how it happened, and Mifune says it's because Hanzo has become weaker.
Mifune recounts their first encounter. When Hanzo confronted a squad of samurai, they fled in fear while Mifune remained to protect them, and even when faced with death. This impressed Hanzo, whom after defeating Mifune, decided to have a personal conversation with Mifune, talking about having faith and bringing peace.
He said that he would take Mifune's life but in exchange would tell stories of Mifune as a hero, but Mifune said he'd trade his life for comrades' safety and Hanzo gave him an antidote to the poison. With that, Hanzo asked if Mifune would rather die with his faith, or live without it. After the story, Mifune asked if Hanzo failed his own test. Hanzo requested that Mifune and the others get at a safe distance and slashed himself across his abdomen, releasing a highly concentrated poison from his poison gland strong enough to subdue him so that Mifune's troops could seal him.
Hanzo has shown to be highly proficient with the ninja basics, such as Exploding Seals and Body Flicker. He was also able to summon giant salamanders, his personal summon being Ibuse. The salamanders, particularly Ibuse, are able to produce poison inside of their bodies which they can store and release, although it takes them 5 minutes to produce more poison after use. Ibuse was also able to tunnel underground and could spring out from beneath the ground to engulf Hanzo's enemy and poison them.
Although Hanzo didn't get to display his jutsus, it was revealed that Hanzo implanted the poison gland of the rare black salamander inside of himself, which died when he was a kid. This gland not only grants Hanzo a superb resistance to poison, but also makes his entire body poisonous, to the point that he poisons the air around him by breathing. Although if the black salamander gland were to be pierced, the concentrated poison it would release would be powerful enough to effect even Hanzo, although not kill him. He also specialized in a kama & chain weapon which too is coated with salamander poison, making a single cut deadly.
Hanzo wore a special breathing apparatus with two functions, one is to filter his poison, but also to breathe underwater which allowed him to fight underwater where his speed was said to be unsurpassed.