>>2596794lol
>>2596805not quite
>>2595816>>2597038passing-through uh, fundoshi enthusiast? here.
You may notice in the art here and in general fundoshi are drawn in many different ways (some of these sort of impossible to replicate or at least unlikely to be done normally, actually. but we won't get into that right now.)
The type you see that has often the rope attached to it is called a shimekomi and it's normally used in festivals such as the hakata gion yamakasa and hadaka matsuri. The rope in the shimekomi seems to be specifically a yamakasa thing, it's called a kakinawa and it hangs from the kakiyama (the festival floats that are carried around in the yamakasa festival) to provide a secure handle to the kakiyama so it makes it easier to carry and also makes it easier to recover quickly if you trip or something. It's just carried in the back of the fundoshi for convenience but really provides no extra structural integrity to the fundoshi or anything as it doesn't really need it since it's tied quite securely around the body already and thus why it works fine as a belt of sorts.