The Japanese legend of Gama Sennin ("Toad Immortal") is based upon the Chinese legend of Liu Hai, a fabled 10th-century alchemist who learned the secret of immortality from the Chan Chu ("Three-legged Money Toad"). Here we see him carrying the golden three legged toad on his back. Gamma Sennin could also assume the shape of a toad. We see him on the ura of this tsuba in that form chasing a butterfly.
This is classic mid-edo Mito workmanship, cica 1750. The quality of the kiko inlay is quite high. Note the kin sabi on some of the gold inlay. A lot of fun to study and well cared for by centuries of owners.