Gomathree evolves from Taikomochi starting at level 31.
Gomathree is a yokai consisting of three mochi-like beings, the lowermost mochi having arms and being larger than the two smaller, more round upper mochis. All three of them are covered in a black sauce, and both of the smaller mochi are drooling the same sauce. The largest mochi holds a large wooden pestle, which it uses to grind the sesame seeds in its equally large red and brown mortar.
Gomathree makes people flatter others like its previous form, but with a twist; the inspiritees take advantage of the person they're flattering, manipulating the ingratiated person to get what they want or get away with avoiding work.
Gomathree challenged Whisper to a flattering challenge, in which Whisper won in every single way possible when Nate summoned the classic yo-kai trio. Whisper treated the three yo-kai with snacks, cleaned them up, and threw out all their trash. This astounded Gomathree who, after surrendering his medal, begins to look up to Whisper and starts trying to flatter him.
"Gomathree" is a wordplay on goma (胡麻, "sesame seeds"), the English three, and gomasuri (胡麻磨り, "sycophant, flatterer".)