On a high school excursion to a science fair in Tokyo, fifteen year old Shunichi Kazayuki was bitten by a radioactive frilled-neck lizard which was on loan from Australia. The impulsive teenager had goaded the lizard and was bitten after extended harassment. He was taken to hospital but no damage was detected. After the initial attention died down Shunichi found himself alone in his grandmother's apartment. His parents had died when he was young and he was being raised by his mother's mother, although the old woman was very weak and confined to sitting for most of the day. The reckless Shunichi became a law unto himself as he entered adolescence and without a firm hand he had become a local street punk.

The lizard bite set off a slow chain reaction within his body, replacing or upgrading his cells with irradiated ones which granted him superior physical abilities. He noticed these enhancements gradually and never attributed them to the lizard bite, but as he reached maturity he realised that he was far more stronger and faster than anyone around him. He decided to make the most of these abilities, which he assumed were uberhuman in origin, and approached the local street gangs which he had admired from beyond.

He was turned away and found himself labelled as a freak in his immediate neighbourhood in Nagoya. The city was fast becoming too small for his interests, so Shunichi moved to Tokyo, leaving his grandmother in the care of her neighbours: something which nearly broke the old woman's heart. In Tokyo he assumed the identity of Yabai, a street name originally used by the Yakuza which meant "heat is on". He had decided that his powers had originated at the science fair and styled his costume on a lizard, giving credit to the anonymous Australian lizard.

As Yabai, he managed to create a stir in the streets, breaking up crime in equal measure to causing general chaos and mayhem. He seemed unsure about what his goals were, but gradually his attention turned to the relatively easy affair of stealing what he wanted. No one seemed willing or able to stand in his way. His natural abilities were a match for the police and the Yakuza, who he had hoped would take notice of him, seemed more concerned in ongoing conflicts and gave him a wide berth as well.

Frustration about being left in the shadows drove him to break into Ichiban Media where he stole a prototype photon mask. He had planned to steal games but when he found the mask he realised that the way to make himself more noticed was to increase his efficiency and capabilities. The mask gave him offensive abilities while also giving him a more cutting-edge look. He continued to break into high-tech facilities in the search of advanced weaponry, but he never really settled on anything except micro-hook attachments for his gloves and feet.

With the return of Senshudan One, Yabai has shown an interest in facing off against uberhumans and testing his abilities against theirs. Although he is not a villain who revels in mass destruction, he is no law-abiding citizen. He has broken many laws and has shown no remorse, apart from using some of his stolen money to relocate his grandmother to Tokyo. She seems to have forgiven him for his earlier betrayal, and thinks that he is working for a media organisation.

Yabai is a happy go lucky thief who is immersed in Tokyo's youth sub-cultures. He is widely known amongst the younger generations of Tokyo and his anti-hero status has inspired several underground manga comics. He has flirted with the idea of being a hero, but much prefers to live by his own set of standards, sometimes leaping to the assistance of Tokyo citizens in trouble, but mostly flying high amongst the silver towers of the city taking what he wants and living life to the fullest.

"I'm the original super-freak!  Accept no gaijin imitation."

Yabai's body has mutated since being bitten by the radioactive lizard, triggering his uberhuman sixth sense ability while also enhancing his physical prowess which has made him much stronger and faster than any normal human. He has shown himself to be a superb hand to hand combatant, mostly because of his uncanny ability to predict opponent's movements but also because of his uberhuman strength which delivers quite a punch.

In addition to his natural abilities, Yabai also utilises stolen high tech gadgets such as his photon mask which can project light in various forms; a functioning radio headset and miniature micro-hook attachments on his gloves and boots which enable him to climb walls effortlessly, seemingly defying gravity.

Yabai's costume is well known across areas frequented by Tokyo's youth. He wears an orange bodysuit underneath a black armoured vest which is trimmed with golden reptilian scales. He wears gloves and boots which are also trimmed with scales, and which have retractable micro-hooks enabling him to climb most surfaces. His identity is obscured by his photon mask which has two very large raised lenses. His hair is exposed and is laced with hair product giving him an impressive spiky look.

Because of the mutation he has a very well defined physique, something he hides in his civilian identity by wearing baggy clothing and trying to look inconspicuous. This is an act, of course, and something he feels he needs to follow in order to maintain his more exciting and flashy 'anti-hero' identity.