Before Madara Uchiha
took control of the Kyuubi
or it became sealed in Naruto
, the Cloud village attempted to capture it to use as a living weapon. Kinkaku
were two of the ninjas assigned to the task, but during the fray they were swallowed whole. Thought dead, they did the impossible and survived inside of the Kyuubi for two weeks, eating the Kyuubi's flesh. They caused such a ruckus inside of the Kyuubi that it eventually regurgitated the two of them, and they emerged infused with a portion of the Kyuubi's power. Others in the Cloud village tried to replicate this achievement by eating portions of the Hachibi, however it only lead to their deaths; it's believed Kinkaku and Ginkaku were able to accomplish such a feat because they're decedents of Rikudou
Thanks to the Kyuubi's chakra, they were able to harmlessly use Rikudou's fabled Five Sacred Treasures.
Many years later, they decided to stage a coup de'etet during the alliance ceremony between the Leaf village and Cloud village, attacking the Second Hokage
and Second Raikage, but failed.
Together with 18 other ninjas, they'd form the Kinkaku Force and chase down the Second Hokage and his group. The brothers would ultimately kill the Second Hokage when he used himself as a decoy for his team to escape.
It's unknown how they died, but they'd be resurrected by Kabuto
to fight in the 4th ninja war. Their presence frightened anyone who knew of them, even the Raikage
had to be talked out of abandoning his duties to fight them personally. They would be confronted by Darui
, Samui, and her brother Atsui.
Ginkaku exchanged swordplay with Darui while Kinkaku quickly showed his dominance over Samui and Atsui, which resulted in them being tagged by the Golden Canopy Rope which drew out their souls, then Kinkaku and Ginkaku switched opponents where Ginkaku cursed the siblings with the Seven Star Sword. Their favorite words appeared on the Seven Star Sword, and seeing that Atsui's favorite word was "hot," Kinkaku used the Banana Palm Fan to burn him, resulting in him being sealed after saying it. Ginkaku was quick to restrain Samui and threatened to kill her if Darui didn't give up, Kinkaku went to strike him but Darui played possum and sliced off Kinkaku's arm, then proceeded to blast Ginkaku with Laser Circus. Kinkaku however still tagged Darui with the Golden Canopy Rope by kicking his arm at him and cursed him with the Seven Star Sword, while Ginkaku sealed Samui since she went too long without talking.
Darui was quick to figure out what his most used word was, however while talking to the brothers he accidentally used two words in sequence that combined formed his most used word, resulting in him being sucked into the Crimson Gourd. But thanks to a loophole, he wasn't sealed because his second most used word became his most used word. Unaware that he wasn't sealed into the Crimson Gourd, Darui used the element of surprise to slam Ginkaku into Kinkaku, resulting him him touching the Golden Canopy Rope, and Darui promptly threw his sword and Kinkaku and grabbed the Seven Star Sword and Crimson Gourd. While Kinkaku was distracted, he blasted Kinkaku with Laser Circus and cursed Ginkaku with the Seven Star Sword. Ginkaku became nervous and called to his brother for help, but his brother's name was his most used word and was sealed.
Enraged, Kinkaku transformed into his six-tails state and attacked, but Darui was saved by Chouza grabbing Kinkaku's gigantic tail. Kinkaku was making short work of the army that were attacking him, so knowing the severity of the situation, the Raikage had his assistant send the Amber Purifying Pot to Darui. It was the only one of the treasures that the Cloud village could recover from the brothers, but that meant Kinkaku knew how it worked so using it to seal him was going to be tricky. Kinkaku tried to blitz Darui before he could try to use the pot, but was saved by Kitsuchi. That's when Shikamaru
, and Chouji
appeared to help. Chouji used his jutsu to ram into Kinkaku, but was tossed aside, however it was revealed that it was only to hide Shikamaru's Shadow Imitation which connected with Kinkaku. This wasn't enough however as he broke the jutsu and attacked with his huge tail, but Shikamaru was saved at the last second by Ino's Mind-Body Switch jutsu. By being in Kinkaku's body, she forced Kinkaku to activate the Amber Purifying Pot's ability and quickly got away as Kinkaku was sealed inside of it.
Madara decided to seal the Kyuubi's chakra within Kinkaku and Ginkaku, so he stepped onto the battlefield himself to retrieve the brothers within the Amber Purifying Pot and and Crimson Gourd.
The brothers possessed Rikudou's Five Sacred Treasures which they would effectively share during battle. Three of the items work together to seal people. The "Golden Canopy Rope" extracts the soul upon contact, the "Seven Star Sword" cuts the soul free and curses them, and upon activating the curse the "Crimson Gourd" absorbs the person; the curse being not to say the word you use the most, although you'll also be sealed if you remain silent for too long or say words in succession that sound like your most used word. Another item is the "Banana Palm Fan," capable of releasing any of the five elements with a swing, and the 5th treasure which was stolen from them was the "Amber Purifying Pot" capable of sealing someone by getting them to respond to you.
The brothers were gifted with the Kyuubi's chakra, giving them a seemingly inexhaustible chakra supply. They could also transform akin to that of Naruto
, sprouting up to six tails and gaining highly augmented strength, speed, and durability.
Since the drawback to Rikudou's treasures is that they require a large amount of chakra to use and prolonged use would kill an average person, having the Kyuubi's chakra allowed the brothers to use the items harmlessly.