OK, what the shit is that device? I have no idea how a circular saw can be applied to anything sexual that isn't guro.

Given the relatively low resolution of the image, it's possible that the 'serrations' are supposed to be smooth bumps, rather than blades. Kind of a 'vibrator-wheel' idea, or something. If I had to guess at the artist's intentions, that's what I'd go for.

As Touhome says, it is based on the same concept of those crotch rubbing rope walking machines, 1, 2 so I do not worry much about guro here.
I do however hope that the blade is supplied with a steady stream of cool lubricant because the friction heat would get SO bad at that speed no matter how soft the bumps are.

So, this is missing one of those squirting metalworking lube systems? Do those even work with waterbased sexual lubricants because I doubt that the non-water stuff is safe for genital use.

Now I kinda want to see a porn series where people have naughty time with converted metalworking equipment.