Ruzoh and Aozo.

Some more backstory/storyline

In a discussion with my s/o, we have decided on some backstory as to why Ruzoh and Aozo can both be Avatars. This also helps explain why Ruzoh is evil and can only see the evil of everything.

To start:

Pronunciation of the names - Ruzoh (Rue-zo). Aozo (A-O-Zo).

Ruzoh and Aozo are relatives to Fire Lord Zuko. Decedents from General Iroh's son Lu Ten. Lu Ten was in his early 20's when he passed away but had connections with a young female before and during the 600-day Siege of Ba Sing Se.

With Lu Ten's death hitting his father and the rest of the nation hard, the young female decided to keep her pregnancy of the heir of the throne a secret. Mainly because Lu Ten and her had affairs before marriage, something frowned upon if performed by a member of the royal family.

The family tree is long and complicated but leads to the birth of Ruzoh and Aozo after Avatar Genji's passing. The twin's parents were both poor Fire Nation citizens. Their father, part of the Fire Nation's restoration projects. Fire Nation officials putting forth effort to upkeep the peace treaty's and policies that Fire Lord Zuko created. Directly related to former prince Lu Ten. And their mother, a non-bender trying to make a living in the Fire Nation. 

Lets go back to before the boys were born. When Genji was alive. With Korra severing the avatar state and creating a new cycle of avatars, the spirit world and the real world were struggling. With this new connection the Avatar had to work harder to learn the skills that prior Avatars would have taught them. Genji being the next in line to do so. During one of his last missions, before he passed, he had to deal with Vaatu. With Raava being weaker after the fight against Unalaq, Vaatu took to seeking out a new way to gain control of the Avatar's elements. He managed to successfully merge with Genji and Raava's spirit. With this successful merge, Vaatu will now be passed on along with the spirit of the Avatar. He successfully gained the power he was looking to gain. But he, also weakened by the fight, couldn't take full control. 

With the passing of Genji, the spirit of the Avatar chose a soul that was strong. This soul split into two during creation, leading to the two spirits to split. Raava, who stuck to the original soul that was chosen, and Vaatu, who attached itself to the additional one. With this, was the creation of  a second Avatar. The spirit attached to Vaatu, born with a pure soul. Not corrupted or in harm. The same with the spirit attached to Raava. 

Fast forward to the childhood of the twins. Aozo, the next in line Avatar after Genji. Forced to learn and train at a young age. Ruzoh, shadowed by his brothers fame. This lead to Ruzoh trying to get ahold of any attention he could. Being raised along side the Avatar lead to difficulties. Ruzoh would occasionally act un-accordingly or interfere with the trainings his brother was receiving. This lead to his parents placing him in the hands of relatives who lived on an island close to Ember Island. This island held a few small villages. A massive forest with a river almost splitting the island into two running through it. Note: Ruzoh was not banished like Prince Zuko was. He could at any time take trips to visit his family, but was only granted a few. Ruzoh growing up at his new home felt lonely. Until he met a girl, who he thought was the love of his life. This girl became friends with Ruzoh, finding out he was brothers to the Avatar, took up a love interest to try and become close to the Avatar. 

When Ruzoh found out that the girl was only with him for his brother, he breaks it off in anger, and goes to the forest to get away from everyone. He makes it close to the center of the forest, close by to a bend in the river, and starts to let his anger out. By mistake, Ruzoh lights a pile of leaves on the forest floor with flames. He notices that its traveling and building at a fast pace. He heads to the river bend to try and bring water over to put it out. With the flames growing at a fast pace, they start to hit Ruzoh's skin. He's not able to contain the fire and panics in fear that it will spread to the village and harm his friends and family. Within the panic he manages to waterbend and put out the flames before they travel far. He is confused at first. But once he realizes, he laughs. "They chose the wrong one" Ruzoh says with anger. Looking back on how he was left out, shadowed, and removed from the place that should have love him and given him shelter; he is overcome by evil. Vaatu, waiting for a moment like this, takes over and removes any good that Ruzoh had within him. Making him a puppet of destruction. Ruzoh trains hard, keeping his discoveries a secret.

Overtime, Ruzoh perfects lavabending. Which he decides is strong enough to defeat his brother. All he thinks about is overthrowing the fame he is receiving. Aozo, who you all know is also an Avatar, fights with his brother, where he finds out that Ruzoh also has Avatar abilities. One's that have not surfaced since the creation of the original Avatar. He manages to save himself and everyone who was harmed in the fight. Ruzoh, thinking he has offed his brother, rises up and claims that he is the true Avatar. Making sure to let everyone know that he is to be feared. Vaatu is here to end the world.