Borrowed 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, […]
2016 June 27, Tejal Rao, “Making Mochi, a Japanese Treat That’s All About Texture”, in The New York Times[1], →ISSN, archived from the original on 15 July 2021:
Ms. Kato, 38, was born in Hokkaido, Japan, and has worked as a pastry chef in French and Japanese restaurants.
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 