The Extinct Japanese wolf (Canis lupus hodophilax) seems closest related to dogs. Dog and wolf split long before 10K years ago, but there was an introgression (mixing) of Japanese wolves with modern dogs around 10K years ago. https://www.sciencedirect.com/science/article/pii/S2589004220311019 https://www.biorxiv.org/content/10.1101/2021.10.10.463851v3

However this study is based on one specimen from recent centuries, which was admixtured with dogs. Still, there is already a clade F of mtDNA in dogs known to have derived from a Japanese wolf.

I'm thrilled because it's my opinion that the original subspecies leading to dogs might have descended from an island or isolated population of wolves related to the Chinese wolf. Much of Sundaland is now drowned due to rising sea levels as the ice age ended.

... Ice age Japan was fused by land bridges and had land bridges to Asia; an icy walk through Hokkado to the Kamchatka peninsula (Siberia, Russia) and a short boat journey from Korea to Kyushu.

Interestingly because of the double connection to Asia, Japan had TWO subspecies of wolves. The Honshu wolf (endemic to the south islands-- Honshu, Kyushu, Shikoku) aka Japanese wolf is what is thought to be closer related to dogs and had crossbred with dogs.

It was distinctively smaller and regarded as good fortune for farmers and travellers. It was appreciated for killing crop-raiding wildlife (rodents, etc.) It was not the smallest wolf; that credit goes to the Arabian wolf, which shares a gene that is found in all small dog breeds (and also Rottweilers, for some reason.)

The Honshu (Japanese) wolf may have arrived at the southern islands less than 20,000 years ago, although the subspecies is older. There haven't been close genetic connections found with modern Chinese wolves, and the study affirms it probably emerged from a Siberian Pleistocene wolf lineage.

However there were many extinct subspecies of Siberian wolves, due to fragmentation and shift of populations caused by the Ice age. The specimens studied here all seem to have branched independently off a common wolf and dog ancestor, despite varying morphology. https://pubmed.ncbi.nlm.nih.gov/33125870/

So the extinct Japanese wolf was probably more related to the extinct Taimyr wolf of Siberia which existed at least 35,000 years ago than the putative extinct chinese wolf ancestor of dogs. https://www.livescience.com/50928-wolf-genome-dog-ancient-ancestor.html

This Taimyr wolf content is found mostly in Northern breeds (which can have up to 15% content) and less so in other dogs.
Speaking of the other wolf-- the Hokkaido (Ezo) wolf (Canis lupus hattai, called the Sakhalin wolf in Russia) had genetic connection with mainland wolves, and was larger and quite distinct from the Japanese wolf. It hunted larger prey in Hokkaido than existed on the southern islands of Japan and looked much more grey-wolf like in size and build. The Ezo wolf went extinct in Japan due to poisoning of livestock predators but might survive on in Russia.

The indigenous Ainu of northern Japan venerated these wolves. They raised wolf cubs and tried to use them for hunting. They were hard to train yet the Ainu would supposedly breed dogs to them, leading to the Hokkaido Inu (or Ainu Ken) breed of dog. These dogs were used to hunt bears and other large game, and also as sled dogs.

https://www.hokkaidoken.org/breed/ Reading between the positive spin code: this dog is dog aggressive, kills small animals, is difficult to train, runs off, and needs careful socialization with strangers. The dog looks a lot more like a chow-chow type rather than the other Japanese breeds. They should be worked/ trained in some way to burn off energy. The breed is around 20 inches at shoulder and 45 lbs maximum, comparable to the Jindo (Korean hunting dog.) They love getting muddy and swimming. They also "talk" like huskies, rooing and singing for a few minutes. Some dogs like swallowing rocks and other non-food items. Submissive peeing may be an issue.

https://www.hokkaidoken.org/breed/history/