Fish is not the only raw food eaten in Japan. Then, sashimi does not have to be always fish. Basashi, sashimi of horse meat is also eaten in Japan, and it is the local specialty of Kumamoto prefecture in Kyushu. Also Nagano prefecture is famous for basashi.
Not like eating ordinary fish sashimi, ginger or garlic will be added to soy sauce instead of wasabi. Ginger and garlic are grated as like wasabi. Chopped scallions are also accompanied with basashi.
The breeding of horses are not so popular as other cattle and therefore most of the horse meat are imported or the horse was brought into Japan and slaughtered. Then, the government is allowing only approved slaughterhouses for the shipping of the raw horse meat. There are only 4 slaughterhouses registered and all of them are in Kyushu, two in southern Fukuoka prefecture close to Kumamoto and another two in Kumamoto prefecture.
By the way, another popular horse meat dish is Sakura nabe; Cherry blossom hot pot.