Netsuke

Ivory netsuke. Character with frog on his back. Has signature: Zipu-Sei. Piece used to attach the inro (box of herbs) to the kimono belt.
The netsuke is a small carved ornament, used attached to a cord and affixed to an inro or to a smoke box, to prevent them from opening. The netsuke could also be a seal, coat of arms, abacus or sundial.