Backstory:
Kikitch was born in a world populated by his kind and infested with a seemingly endless horde of monsters and horrors. The society he was born into had barely reached their iron age, and even with iron weapons the blight that had come upon this world was suffocating it.
He was barely 12 years old when one such monster attacked, ravaged and devoured most of his village, only being saved from such a fate by a witch named Mina when she crippled, paralyzed and absorbed the beast before it could find him.
After it became clear that Mina meant no harm to them, the survivors of the attack and Mina worked on learning each other's language as Mina mended the few injured that could still be saved, with Kikitch being the fastest learner from among them.
They were told by her that she was from another world, and that their world had most likely been forsaken by their creator, seeing as the eldritch monsters infesting it were coming from the Abyss between worlds itself. She also told them she had come here to hunt said monsters for their power and that she was merely sixteen herself.
She help them rebuild as best they could by sticking around and letting the noise attract more monsters, claiming it was merely a convenience for her to have what she was looking for come find her. When the works were done a few weeks later and she was offered anything she could ask from them as a reward, she quickly made up her mind: She wanted Kikitch to come along with her, as a student and a traveling companion.
While it wasn't what he had expected, he agreed to her offer, having realized in that moment that there was nothing left for him in his world anymore. It was shortly after their departure when he would choose a new name for himself, inspired both by Mina teasingly calling him Matthew and his first attempt at pronouncing "banish" while learning English with Mina: Matthew Bramish.
The two of them would grow up together and Matthew, while much to Mina's disappointment and pity, proved to be utterly incapable of casting magic, was a prodigy Rift navigator, quickly picking up on the patterns and signs to look out for. He was also a studious scholar, a great forager and a capable tracker, while Mina was a great help for Matthew to adjust to life within cities and as a traveler on the roads.
That's not to say their relationship was perfect: Mina would toy with Matthew with her magic and Matthew would often get them into trouble by failing to make sense of one or the other law or custom, but they pressed on and grew closer in time.
Eventually, Mina and Matthew ended up in a modern world and Mina decided to settle down for a while after seeing how nice it was to have running water, electricity and internet access for the first time in their life. Having already reached adulthood herself, Mina also started... "experimenting" with her sexuality, though it's more accurate to say, her mountain of kinks.
After walking in on Mina playing with a "toy" Matthew grew both repulsed by her behavior and intrigued by the idea of having someone sealed inside of him, culminating in him making a plan to enable him to indulge his desires. Though he promised himself he would make sure no one would be harmed by it.
It would take over two years of hunting and capturing monsters for Mina to transmute into the necessary mutagens to complete his transformation, and that was after he sought out some alterations to improve his strength, constitution and speed. He was 21 years old by the time he was finally done and underwent a complete remaking of most of his abdomen, promptly testing his newfound predatory ability on Mina. A move that would both earn him the witch's respect as an equal and mark the start of Matthew's descent into hedonism.
In the time Matthew had spent hunting beasts Mina had found a highly lucrative job as a plastic-less plastic surgeon, initially dealing with high profile mobsters and the criminal underworld and gradually building connections till she could open her own clinic in broad daylight... and she was raking in the money like never before. Money she invested in high end gear for Matthew along with huge bounties on some of the most coveted lost magical artifacts across the whole Nexus. Matthew was in his element... and was blowing through money like a drunk millionaire on his vacations in between his bounty hunts.
It was only when Matthew was confronted one fateful night by some cute deerboy as to why he was eating him, why he couldn't look him in the eyes... why he wouldn't stop did he realize he couldn't stop. Couldn't will his hands to let go, couldn't stop scarfing him down. It was only then that he realized his habit had long since turned into an addiction. And a long, deep self loathing for what he had become set in.