There is a restaurant in Obihiro called Pancho, which has been in business since 1933, and the butadon is said to have been devised there by its first owner.

Thick-cut pork loin is grilled slowly over charcoal, so a faint smokiness stays in the meat, and then a dark sauce of soy and sugar is worked over it before the slices are laid across a bowl of rice. Not simmered in a sauce, not battered and fried. Grilled over coals, then glazed.

The reasoning behind it was economic. Pork hotpot and pork cutlets were expensive dishes at the time and out of reach for most people in the town, and a donburi was a way of getting the same protein onto a plate at a price that worked. Tokachi was pig-farming country to begin with, so the raw material was already close at hand and cheap.

What the dish is really doing, underneath all of that, is substituting one animal for another. Eel was the prestige thing you grilled and glazed and put over rice, and it was far too expensive, so pork went into the same procedure with roughly the same sauce. Nearly a century later the substitution carries the town's name, and the color of the glaze is the part that remembers the eel.