Haruki's Lunarian nature should give him some sort of edge in dealing with metavores. He will lose his job for a while because of this, just before the finale.
The distinction between the Plexicols and Haruki's society is that Luna's socialist "bureaucracy" is not impersonal. All citizens are highly engaged at every level, as a matter of both culture and compulsory civic duty. The Terran system is "voluntary" and decentralized, but totally depersonalized, prohibitively difficult to change, and opaque to most citizens.
Exploit the voodoo-like, arbitrary nature of modern post-industrial capitalism. The transmodern economy should not function by rules knowable to the average citizen. They're so complex and abstract, they can only be understood intuitively or by very highly trained experts. This puts economics even closer to the realm of religion...
There's a subculture of metagamers who, like Haruki later in the series, have been "disappeared" by a system glitch that gets them mistaken for defeated metavores. They've evolved a culture of their own that is completely, ingeniously devoid of abstractions, a third alternative to Lunarian and Terran society, free of linguistic "poisoning," bordering on a new form of consciousness barely comprehensible to outsiders.
The rest of society has noticed the disappearance of some of its metagamers. People are aware that metagame technology is capable of making people disappear, and they realize that some such people may walk among them, but they're resigned to never being able to find these people since by default they're unfindable. This could be made an allegory of why a cultural fringe is useful -- fringe groups might have an economic niche devoted exclusively to experimenting with recovering these "lost" people.
What is the scope of each metavore's threat? Citywide? Worldwide? Streetwide? How many direct competitors does Haruki have? Are there many threats at various Mazslovian levels, or is Haruki working through them like a class/level system? Do people know openly that the metavores are assigned Mazslo's hierarchy levels, or is this just an unspoken theme?
The metavores are tulpa-like, reacting in an unpredictable feedback loop to people's responses to them. The population is aware it's being manipulated but can never be sure where or how -- that's part of the fun!
Metavores should be subtle, eerie, conspiratorial... Think of Buffy, and how the various supernatural Bads are all allegorical of teenager problems.