I figure the most direct way to do it would be to replace youkai with battle robots that became sentient (for some reason only the android models show up on-screen), and magician youkai with full-body cyborgs. Other characters who turned from human to youkai would be the result of uploading their minds into robot bodies. Lunarians are genetically engineered I guess, through a process invented by Eirin.
Rinnosuke would be a guy with cyborg eyes that can scan things, while Youmu would have cyborg limbs that make her super-fast.
Unzan is an antiquated, bulky robot that can't speak, which Ichirin found in a pile of scrap and decided to repair.
The Saigyou Ayakashi is a supercomputer that runs everything in the Hakugyokuro district , with an AI named Yuyuko that can project itself as a hologram. Yuyuko was originally a human whose consciousness was uploaded into the system, but the process was flawed and damaged her memory.
Mamizou is an infiltration unit - it's well known that her model has terrible specs due to the room needed for all those image projectors, but Mamizou herself is so skilled that she can take down far more advanced machines with ease.
Seiga is a notorious hacker who can pass through any firewall. She also deals in weird drugs that can really mess with your brain - poor Yoshika started on the weak stuff, but now she can't even go to her poetry sessions any more. All attempts to put her behind bars have failed - whenever the feds get too close she just changes her name and moves to a new location (she's even faked her own death once or twice).
The Miracle Mallet is a computer virus which only Sukuna knew the password to activate.
Miko is a genius engineer who can work on ten projects at once. A child prodigy, her school project was a set of small robots with primitive AIs that could communicate with each other, allowing them to learn more and more complex behaviours by working together; she had no idea that it had learned to seek out power sources on its own, that it had kept evolving for more than a decade...