Prologue

Tadashi Hamada couldn't really remember the last few moments of his life in any detail. There had been heat, and light, and smoke filling his lungs until he was choking on it. He faintly remembered something falling from above and hitting him in the head, knocking him to the ground and leaving him stunned. There was a period of darkness and uncertainty, and then he woke to the smell of burning flesh and searing pain all over his body. He remembered looking up, and seeing someone standing over him, though he couldn't make out their face through the smoke and the tears in his eyes. Then, there was more bright light, and pressure and noise and pain.

And then there was nothing.

Robert Callaghan remembered the last few moments of his life clearly. He remembered staring down at his favourite student, pinned beneath a fallen beam and slowly burning to death. He remembered feeling mild pity at the waste. Tadashi had always been such a brilliant, hardworking student. But not as brilliant as he'd thought apparently, if he'd been stupid enough to run into a burning building and get himself killed. Even though he wasn't dead yet, Robert was sure the boy would sucumb to his injuries soon enough, and he didn't have time to help. He still needed to retrieve the neurocranial transmitter for Hiro's microbots if he wanted to take them and use them for his revenge. Krei's presence at the showcase tonight had only furthered his desire to destroy the man who had taken his daughter from him. So Robert turned away from Tadashi and his whimpers of pain, already dismissing the boy from his mind as he went to retrieve the headband that laid abandoned on the side of the main stage.

But Robert hadn't realized how quickly the fire he'd set had spread, and he'd failed to account for the large tanks of compressed air that had been set aside for one of the devices that had been shown off earlier in the show. Before he'd known what was happening, the tanks had exploded with enough force send a shockwave through the building that leveled everything that hadn't already been destroyed by the fire.

Robert wasn't sure if it was the explosion, or the shrapnel, or the roof collapsing that actually killed him. Either way, he'd woken up afterward to the sight of his own body below him, and immediately knew he was dead.

At first, he'd been upset, as was natural for someone who'd just died. Then he'd started wondering why he was still here, and if this truly was all there was to life after death. He'd never been one for religion, but he'd always assumed that there was at least something beyond. This was not what he'd expected at all. But then it occurred to him that if this was truly the afterlife, then surely Abigail would be here with him, wouldn't she?

But she wasn't, that he was quick to see. Perhaps she wasn't here, he thought, because she had died in some strange portal that Krei had created, leaving her trapped in some other world. Robert felt his heart clench in pain and despair. Even in death, his little girl was lost to him.

Almost immediately his old rage returned, burning away the shock of his death and his grief. The rage was familiar, comforting, and he clutched the emotion to his chest like a lifeline. He was dead, but he refused to move on until he'd gotten his revenge. He refused to pass quietly into the night while Krei still walked free.

His mind then went to his original plan, stealing Hiro's microbots and using them to get his revenge, but he almost immediately discarded it again. He doubted the neurocranial transmitter would work for a dead man. Such a pity, considering all the effort he'd put into starting the fire to cover his tracks in the first place. Such a waste. But he was flexible, and patient, and absolutely driven by his need for vengeance. He'd think of something else. He would find a way to make Krei suffer.

He set his mind to working on new plans for revenge as he started to walk away from the ashes of the showcase hall, and the remains of his life, already deep in thought. But when he reached the gaping hole in the wall where the south corner of the building had collapsed in the explosion, a flash of white caught his attention. It was like a beacon of white in the dark ashes of the hall, immediately drawing his eye like a moth to flame. Curious, despite himself, he bent down to try to pick the object up from where it was half-buried in soot.

It took a few tries to get it free. He'd forgotten for a moment that he was nothing more than a ghost now, completely intangible, and had been rudely reminded when the first time he tried to touch the object his fingers had passed right through. But something told him that he needed to see what it was, and so he didn't allow that to discourage him. With a little trial and error, he found that if he concentrated, he could make contact with it, and once he found purchase he pulled the object loose with a tug. Slightly tired from his exertions, but feeling quite pleased with himself regardless, he held the object up to the pale moonlight shining through where the roof used to be to get a closer look at it.

It was a Kabuki mask. He wasn't sure what such an object was doing at a science fair of all things, but they weren't exactly rare items in this city. The golden eyes stared up at him almost accusingly as he traced his fingertips over the red painted lines. He had never been much of a fan of the Kabuki art form, despite its popularity in San Fransokyo's theater districts, but he'd picked up enough about it simply from living in the city to recognize the design as a hero's mask. Immediately his mind went to the comic book superheroes he'd practically worshiped as a child, the heroes disguising their identities as they gained vengeance on the criminals of the city. He chuckled to himself as he stared down at the mask. It was almost too fitting, a voice whispered in the back of his mind. It's perfect.

With a satisfied smile, he placed the mask over his face as he headed out into the night. Even if he was dead now, he was determined to find a way to take down Krei and get his revenge, revealing the man for the true criminal he was just long enough for Krei to suffer as Robert had suffered.

And then he was going to make Krei join him in the afterlife.

Robert was so focused on his thoughts of revenge he didn't notice the shadows of the building suddenly thickening around him like a living thing, a sound like the faintest whispers growing from within them. The darkness shifted as he crossed the threshold of the ruins, moving and flowing along the floor and through the rubble like liquid smoke to spread across the entire area. As they travelled, they started absorbing every one of the discarded microbots that had been scattered from the explosion, pouring into all the cracks and crevices to ensure they didn't miss a single one. Robert didn't notice this, nor did he see the shadows coalesce into solid tendrils once they were finished absorbing the microbots. They started following him like a loyal dog, the whispering noises becoming stronger. He also couldn't see the green and purple veins spreading across his body like a virus as his mind became consumed with nothing but the desire for revenge.

Robert was luckily also too distracted to see a soft glow suddenly appear hovering over the ashes of the showcase hall, a trio of ghostly blue flames swirling around it like moons as it slowly started to take human shape.

By the time the ghost of Tadashi Hamada had fully materialized, Robert Callaghan was long gone.

AN: AAaaaa finally, this is getting to be posted and I'm so super excited! This idea was the spawn of a ghost!au I thought of, that my friend Cake (url ikiracake on tumblr) then grabbed and worked wonders with. Written mainly by Cake, and crossposted on AO3 with illustrations (drawn by me) in later chapters. Illustrations can also be seen on my tumblr at url machina-rex /tagged/bh6 ghost au

Hope you all enjoy! Please review to let us know what you think!