Over here it would be a Pine Martin. They have a bunch of them up in the northern states like Minnesota. It's in the weasel family and can out climb/out run and catch a gray squirrel all day. Squirrels are their main prey, I don't know what the Japanese version feeds on. I guess they have squirrels of some sort too. I dunno.

[ame]http://www.youtube.com/watch?v=9-HxtOaGzWA&[/ame]