a Chinese violin of sorts, but the bow isn't supposed to be able to become detached to the actual violin.
But that would make it really hard to draw action scenes with it wouldn't it?
Still, and Erhu is to be played positioned vertically, usually on the lap, with the bow positioned horizontally near the end of the instrument. Seeing Rin being depicted with a violin grip on an Erhu seems to betray the knowledge of Erhu that Rin would actually have.