Warning: Bear Activity
Hokkaidō is bear country. The bears up here are different to the small black bears that inhabit Honshū; these are higuma (Ussuri brown bear), thought to be the ancestor of the North American grizzly bear, and they're much bigger and more aggressive.
Take all precautions, especially in the early morning and at dusk, and avoid hoofing it alone. Make a lot of noise; like Japanese hikers, tie a kuma-yoke (bear bell) to your rucksack. The theory goes that bears want to meet you face to face about as much as you want to meet them face to face and if they hear you coming, they'll avoid you at all costs.
If you're camping, use the steel food bins or tie up your food and do not bury your rubbish. Bear activity picks up noticeably during early autumn when the creatures are actively foraging for food ahead of their winter hibernation. Be especially cautious at this time.
The Shiretoko peninsula is home to the highest concentration of higuma on Hokkaidō, but they are also often sighted in Daisetsuzan National Park; really, they could be anywhere there are mountains. Only the remote islands of Rishiri-tō and Rebun-tō are bear-free.