This is a good explanation, thank you.

I've rented cars frequently from Toyota and what we know as LDW was always built into the rate, but there was a deductible. Oddly enough, I was never offered any other insurance to offset the deductible, but Y20-30k is not too much to worry about and I never bothered to think more about it.

The more important question is any foreign renter's experience and ability to drive and navigate on the "other side of the road" in a different language (even the english GPS spits out names in super-fast Japanese) safely and comfortably, which is the primary issue before renting a car in Japan.