From wikipedia, “Mochi is a Japanese rice cake made of glutinous rice pounded into paste and moulded into shape.” Given it’s name, the most logical guess would be Mochi originated from Japan.
The shocking truth is Mochi originate from an aboriginal recipe in Taiwan. It gained popularity and the Japanese royalty loved it so much that they gave gold medals to Taiwan for the invention of Mochi and soon started making their own.
Some confectionaries in Taiwan have queues that are snakelong. The mochi are made fresh and best eaten within 24 hours.
Got this fact from a documentary on National Grographic.