Suika as the yukkuri equivalent of boars? That's original alright.
You know, I never could understand the desire of some people to run over things. Some even would deliberately tie animals and run them over >_> If yukkuris were real, I suspect they'll be a favorite of these kinds of people as well.
Considerring how yu are soft, wouldn't a bih enough one cause a loss of traction?
Suikas can control density and that means they can get to become so dense they are invulnerable to physical damage.
Now, a big enough regular yu like a fat reimu or marisa if squished by car tires, will probably cause the tires to lose traction if the threads are worn enough to allow such a thing to happen.