Hi Arjan,
Yesssssssssssss, Ainu it is !!!
Sorry, but this illiterate soul never heard of ainu.
And I am afraid I am not the only one on the forum
However, the mix between rough material such as antler and the japanese / samurai style explains why I once had a pipe container that was roughly made of antler, with the carving of a rough but otherwise traditional crane bird. Probably that one was ainu too
The tip of the blade might have been broken of long time ago.
Looks old.
Ps. the carving is really nice, better than those on the website you found.
Ps. 2 : Any Ainu experts around on the forum, for an educated opinion ?