The Caraxi family owns safehouses spread over a considerable amount of land for such a small entity. The main ones, the largest, the most ostentatious are often empty, cold, dully polished by hired help and otherwise left untouched. The smaller ones, the inconspicuous ones, the ones with an anonymous air to them, are those where these magi are most likely to be found. That's because their magecraft requires sacrifices. Plants, rocks, animals, anything works. Humans without prior knowledge of magecraft are strictly off limits. However, the strength of the family's magecraft varies depends on what was sacrificed. Therefore, other magi are the best prey of all.
Even if the disappearances that follow their activity are found out, they're unlikely to be connected to the Caraxi's scattered network. As a matter of course, large swaths of the Caraxi family are unaware of the activities of the other branches, and even within the same travelling nuclei, those demanding the nucleus to move might not need to disclose their reasons at all.
Adiwa's youth was spent travelling across the world. As wonderful as the sights were, most of the travelling was so he could help mutilate or kill for this or that relative so they could advance some scheme he knew nothing about. Travelling was often close to an annoyance, then. Adiwa became numb to taking human lives, and assigned them little value. Even so, he wanted to be useful. Not just that—he wanted to be useful beyond what he could do for the family that so liked to keep him in the dark.
Eventually, a more respectable branch of Adiwa's family became well-connected enough that he could indirectly learn about the thwarting of the Incineration of Humanity.
Perhaps he could make himself useful, after all. Not by destroying humanity, of course, but...
He began to actively hunt on his own, as a member of the Caraxi would. He targeted seven powerful mages. Ones he could barely beat by the skin of his teeth. Finally, he channeled those seven.
He was unsure it would work, but what difference did it make, anyway?
A spiral of eyes that had been looking for a way out, for an escape, all this time, finally burst forth from the last sacrifice... Only to find itself much weaker than expected. As if, rather than escaping certain death and recovering, it had been condemned to languish eternally. Unable to leave. Nailed in place.
"Don't worry, I'm going to destroy humanity for you," he told the Demon God. Of course, that wasn't Adiwa's real intention.
He'd needed some powerful sacrifices to bring the wonded escapee here, and to prevent it from perishing. However, he hadn't enhanced its condition all the way to restoring its full power. In fact, he had enhanced the Demon God precisely up to the point to which it could create Holy Grails and displace him, but not enough that it would be able to leave the newfound cage in which it had been lured.
Like so, Adiwa got the Demon God to displace him to another time and place. There, he summoned a Servant that could enhance the mystery in a certain area, though without making it any easier to control for anyone. After doing so, Adiwa supplemented his Servant's ability with his own compatible magecraft by killing Servants summoned by Proper Human History. Then, Adiwa gave the grail to king Menander, an inhabitant of the new Singularity. This led to the resurgence of a certain Divine Spirit,
Menrva...
In any case, Chaldea took care of that Singularity. Before escaping, the excuse Adiwa gave them for interfering with Proper Human History was that he wanted to see the full potential of humanity and then destroy it. That wasn't exactly right. He really was hoping Menrva, or any of the situations resulting from his meddling, would ultimately bring some form of eternal salvation. But more specifically, regardless of how many recipients of his Grails were to fail, his plan was to accumulate enough sacrifices so that with the help of his Servant he ultimately could...
⫷⫷╋╋╋⫸⫸Enhance the Throne of Heroes itself. In his projections, this would've been sufficient to create a backup that included all of humanity, but made exclusively of their better aspects. Every human would've become a Heroic Spirit of the same strength, no matter how legendary or how irrelevant in the eyes of others. The enhanced Throne would've then been made to spill out onto Earth, or otherwise created a society within itself, or... Or something else would've happened to lead to harmony, right? There was no true guarantee any part of the plan was going to work exactly the way he wanted. But, after all, he just wanted to try to feel useful.