The living mochi with a face (we think) that appears on the title screen of Touhou 15: Legacy of Lunatic Kingdom. It appears nowhere else and is never mentioned
again even once, the one major stretch of an exception being the LoLK difficulty selections, which are all captioned with degrees of mochi firmness.
Despite this, or even perhaps because of this, it has become a minor fandom meme. Fans think it's a mochi with a face, but there is no unanimous consensus, so its name is sometimes a variation of "Mochi...?"
Fans seem to enjoy giving it cameos in unexpected places, especially where it goes unnoticed by every character in the picture. Its exact smiling face design would later appear in Touhou Lost Word on the common Phantom enemies.