Rune was born in Hell thousands of years ago, into one of the most strongest demon families. However, once he was born, the power he was born with was too much for his small body. This was expected however, and a ritual was performed immediately after he was born. Rune was born into a demon race known as the Oni, due to masks being a major part of their livelihood. The ritual consists of transferring most of the Oni's power into a mask, making it so that the child survives their first thirty minutes of life.
As Rune was growing up, he started to hear the mask speak to him. The mask explained to Rune that due to the immense amount of power that was transferred to him, the mask became sentient. It also identified itself as Faust. Rune went to get an explanation from his family, and they told him that this was common for their kind. They also explained to him that no matter what to never put the mask on, only for extreme life or death situations.
As the years went by, Rune became extremely bored living in Hell, despite being one of the most powerful demons and living in luxury. Rune went to the Human Realm, at first just to get a change of scenery and a fresh breather. However, he ran into something that he wasn't expecting to run into: Humans. He discovered a human city called Pompeii, and couldn't help but explore. With Faust tied around his neck, he was definitely the center of attention, as everyone has never seen the craftsmanship of the mask before, along with Rune being taller than even the most tallest man there and his unnaturally silver hair.
As he was walking around, he accidentally bumped into one of the humans that wasn't paying attention, watching as a young woman fell to the ground. He apologized to her as he helped her back to her feet, and as he got a better look at her, he was struck by her beautiful appearance. She stood shyly as Rune observed every part of her physique. Her green eyes shimmered as her long brown hair gently blew gently in the breeze. She attempted to apologize to him, but he didn't understand the language she spoke, but he was very much interested in her. He attempted to apologize by getting her flowers and food. She was skeptical at first, but as she took his gifts, her lips curved into a small smile. She looked at Rune and simply said to him, "Agata." He figured that was her name and watched as she walked away.
After this encounter, Rune made it a point to see her as much as possible. He went to see her everyday for several months, and during those months, he was able to fluently speak the Roman language, learn about her people's culture, beliefs, and about her life and her family. The closer they got, she got more curious about who Rune was and where he was from. He ultimately told her who he was, and was surprised to see that it didn't seem to phase her, keeping the same smile on her face as she expressed how deeply she cared about him. After confessing his feelings for her as well, they shared an intimate and passionate night together.
They spent another week together before Agata's family found about their forbidden relationship, and forbade her from seeing Rune again. Rune didn't react to the news very well and went to explain himself, however as they continued to argue, Rune's anger got the better of him and Faust reacted to Rune's emotions, and his eyes started glowing bright red. Scaring Agata's family, they accused Rune a monster and Agata a witch as well as attempting to kill their family. Nearby guards over heard the commotion and reacted appropriately when they saw Rune and Faust's glowing red eyes.
As they attempted to attack Rune, Agata stepped in front of him attempting to protect him, resulting in her getting stabbed in the stomach and slashed along her throat. Rune quickly lied her down on the ground, watching as despite her current situation, she looked at Rune with a smile on her face, telling him how much she loved him one last time before dying in his arms. Enraged, Rune looked at everyone as he grabbed Faust and brought him onto his face. This was the last thing that he remembered, as he finally came too, he saw Pompeii completely destroyed and watched as the lava from the volcano flowed onto the city, as the air was filled with ash. He looked around and saw that Agata's body was untouched. He gave her a proper burial and said his final goodbyes.
After this, Rune spent most of his time back in Hell, only to return to the Human Realm once every one hundred years just to see what has changed. It wasn't until after the failure of Y2K that Rune decided to stay on Earth. During his time back on Earth, he grew to enjoy the company of Humans, and doesn't enjoy when demons come to ruin his fun.
Personality
Rune is best described as a sarcastic asshole with a heart of gold...well...not really. Although he enjoys the company of Humans, he will not hesitate to correct their "unwanted" behavior. However, he becomes suspicious when demons are around, believing that they are going to ruin his fun or harm the humans in some way. He acts more like an Anti-Hero than anything else, and is prone to anger.
Powers
While not wearing Faust, Rune's power is limited to only 40% of his true potential. He is super strong and super fast, and is able to manipulate flame sources, but isn't able to conjure any form of flames by himself. He is also able to regenerate wounds, although its not as fast as it is when he is in his true form.
However while Rune is wearing Faust, not only is he able to access 100% of his power so he is much faster, stronger, and able to fully breathe fire and control and manipulate it's properties, but his true form is also revealed. While in this form however, he is more prone to his anger, and if he gets angry enough, then he goes feral, which can last from a single day to several weeks. During his Feral Rage, he is not in control of his actions, and he will destroy anything that is in front of him. Those that have seen Rune in his true form have not lived to tell about it, and that's how he intends to keep it.