Working as a reporter for an unnamed news magazine, Masaki Murakami (村上征樹) first came to the attention of Chronos when he and his team went to New Guinea to research the culture there. When they decided to investigate the rumors of monsters in the deep forests of an as-yet-unknown portion of the island, they inadvertently stumbled upon one of the sites where Chronos tested their Zoanoids.
The other reporters with him were all killed for one reason or another, but Masaki himself was spared; reasons for this have not been stated in canon, but speculation tends to be that Masaki was determined to be compatible with Chronos' processing methods. How this was accomplished has still not been stated in canon sources.
What is known, is that Masaki was taken to Chronos' main headquarters in Arizona, to be part of the processing experiments that they were conducting. The ultimate aim of these experiments was the testing of the abilities and needed genetic-modifications to one Richard Guyot, who was to be the final member of Chronos' Council of Twelve. The test subjects used, Masaki among them, were slated for immediate disposal once the end of their usefulness had been reached. However, this was not to be.
One of the scientists who had been put to work on the project, a man named Shinichiro Yamamura - having long ago decided that he would oppose Chronos in any way that he could - released Masaki and the three other Zoalord prototypes from their tanks. With the knowledge that he possessed on Chronos and their operating procedures, Yamamura was able to advise them on the best places to strike. However, their primary target was Richard Guyot, the Zoalord who their lives were being sacrificed to create.
However, not one of the Proto-Zoalords (獣神将試作体) present would manage to kill him.
The appearance of the Council of Twelve put a permanent stop to Yamamura's plans, and the good doctor himself was killed not soon after. The Proto-Zoalords themselves, save for Masaki, were rounded up and disposed of as well. Masaki, who had the least injuries out of the three, was aided in his escape by Yamamura, and likely the other prototypes as well.
Leaving the Arizona base through as-yet unknown means, Masaki returned to Japan. Taking on the guise of a reporter, his job before he had encountered Chronos in the first place, he kept watch on them from the sidelines, likely knowing a great deal about what they were planning. Though he knew that being processed into a Proto-Zoalord had drastically reduced his lifespan, Masaki was determined to stop them by any means he could.
He also knew that utilizing the battleform he had been granted would shorten it even more.
Masaki first appears before Sho when the latter has been cornered by a group of Zoanoids. The Zoanoids manage to capture the young Guyver by deceiving him into thinking that they had managed to capture Mizuki. Sho, unable to hurt someone wearing the face of a person he cared deeply for, was fully prepared to go along with them to ensure that they wouldn't harm her.
However, given his ability to sense the presence of Zoanoids, Masaki was not so easily fooled. Revealing the ruse to Sho, Masaki left the boy to deal with his enemies while he drew one of them off. Intending to interrogate the creature, Masaki was surprised and dismayed to see Sho slaughter it before he could find out what he wanted.
After having escaped the main headquarters of Chronos, Masaki went into hiding in Japan, biding his time until he could get his hands on one of the Units stored there. These plans of his, however, came to naught. The three Units had already found hosts, and Lisker was long dead at that point.
Masaki in the Anime
Masaki, seeing that he would never have the opportunity to gain a Unit of his own, decided instead that he would help those people who did have them. When he first encountered Sho, it was during a fight with Aptom and his fellow Lost Numbers. Masaki lent his aid to the young Guyver, acting to distract Dyme from an attack on the boy, but inadvertantly getting captured himself.
With another person to protect, however, Sho found new resolve and was able to successfully fight off the Lost Numbers attacking him.
After doing so, Masaki was quick to support him in his endeavor. Sho, having been shocked by the revelation that his friends - not just his father, as he had initially been lead to believe - had been the targets of Chronos' forces, was all but ready to give in to their demands for his surrender. Stepping in just as Sho was at his lowest, Masaki reassured him, explaining that Chronos was not just a threat to his family, but to every human being on Earth, a fact that Sho had come to realize some time ago, but which had been almost completely forgotten by the boy in his anguish over his missing friends and family.
Taking Sho under his wing, Masaki told the boy about another Chronos base in Japan, one hidden deep underground and stretching for miles in several directions, Mt. Minakami. With the help of the young Guyver, Masaki was able to find a way to infiltrate the Mt. Minakami facility. However, that would come later; for the moment, Sho's focus was on rescuing his friends and his father.
With Masaki's help, Sho was able to trace the mental signals from the third Guyver - who was, unknown to him at this point, Agito Makishima - to Mt. Minakami itself.
Transformation into Imakarum Mirabilis
When Guyot destroyed his dummy Zoacrystal, Masaki was left either dead or in a death-like state, at the bottom of an erupting Mt. Minakami. Luckily - or unluckily, depending on how one looks at things - he landed at the feet of Archanfel, just after the Supreme Zoalord had finished disposing of the traitor Richard Guyot.
With Guyot's Zoacrystal still clutched in his hand, and a dying Proto-Zoalord at his feet, Archanfel was not slow about taking the opportunity that had been presented to him. Bringing the comatose Proto-Zoalord with him, likely to the Dead Sea Plant with the Relic remains, Archanfel, Dr. Barcas, and an unknown number of other scientists and laboratory technicians began the process of transforming him into a full Zoalord and ensuring his loyalty to Archanfel.
What this entailed, how long it took, and the specifics of the alterations made, are all completely unknown at this time.
However, Imakarum Mirabilis (イマカラム・ミラービリス) is completely loyal to Archanfel's cause and the ideals of Chronos, even attempting to recruit Sho on their first meeting, when Sho and Agito had attempted to invade Cloud Gate.
Needless to say, this offer was firmly - or in Sho's case, not quite so firmly - rejected, and Imakarum, with what seemed almost like genuine regret, turned his power to the task of eliminating the threat that the two Guyvers posed to Chronos and its master, Archanfel. Attacking the two Guyvers in his human form, Imakarum would have likely been able to kill at least Sho, if not for the timely intervention of Aptom. The Lost Number was adamant that the life of the young Guyver belonged to him. Imakarum, not caring for the peculairities of a mere Lost Number - and having heard of Aptom before - attacked them both.
Aptom barraged him with missiles, but Imakarum's barrier repelled the attack, causing the missiles to detonate against it rather than doing any harm to Imakarum himself. The next one to make an attempt on the Zoalord's life was Agito, who had been hiding in the building that he had been blown into after Imakarum's initial attack. His attempt on Imakarum's life ended in the same failure that Aptom's had, but he did manage to destroy the Zoalord's visor, letting all of the combatants see the most obvious signs of Imakarum's re-processing: his yellow, slitted eyes.
After this change had been revealed, Imakarum quickly transformed into his battleform. Sho, still anguished over the fact that he was being forced to fight someone that he still cared about - someone who had in fact died in his arms - was unable to fight him at first. Sho even tried to reason with Imakarum at the beginning, attempting to remind the Zoalord of all that they had been through together in the hope of bringing him back around to their side.
It was completely for naught, however; Imakarum remembered everything about who he had once been, he simply didn't care.
Attacking Sho with all the more ferocity for the time he had taken to listen to Sho, Imakarum drove both Guyvers toward Tokyo bay, while Fried'rich van Purg'stall watched calmly from his post in Chronos' Cloud Gate.
Being far more powerful than his previous incarnation, and wearing the face of someone Sho had trusted with his life, Imakarum truly only had to concern himself with the attacks that Guyver III made against his person. Sho Fukamachi was far from a threat at that time. Even with the Gigantic at his disposal, the boy could not muster the will to fight Imakarum.
Imakarum knew this, and intended to take full advantage of it.
Unfortunately for him, Agito Makishima managed to take control of the Gigantic Armor instead, and showed no hint of Sho Fukamachi's restraint in fighting his former ally. Imakarum was very nearly beaten to death by the Gigantic Dark - literally, his Zoacrystal cracked by a hypergravitonic punch - and only survived because Archanfel, sensing he was in distress, came to save him.