From Japanese北海道(Hokkaidō, “North Sea Circuit”), from Middle Chinese北海(pək-hʌi˧˥, “Northern sea”) + 道(dáu, “Circuit”, a province-like administrative unit from Tang dynasty China).
2009, Nicolas Tranter, The Languages of Japan and Korea:
In the past, the Ainu (their selfname meaning 'person'), traditionally huntergatherers, occupied not only Hokkaido but also a considerable part of the island of Honshu until the middle the eighteenth century, […]
2019, Supana Onikage, translated by Quof, edited by K. “Kitty-tama” Jordan, Lazy Dungeon Master, volume 5, J-Novel Club, →ISBN:
I took another look at the map, impressed by how useful random modern Earth knowledge was in this world. Tsia Mountain, which contained our dungeon, was within the Empire’s territory. Using the size of the mountain to estimate distance… Yeah, the Empire was pretty huge. How many Hokkaidos could even fit in here? More than a few. Not to mention that there’s dozens of dungeons marked on the map.
Hokkaido on Wikipedia.Wikipedia 