This is Tororo, the idea of twisting yamaimo/nagaimo over a fine grater and getting a sticky and gooey potato that can be eaten raw. In China it is considered a medical food but in Japan its called Nagaimo and seen below it is mixed with rice and seaweed and some fermented pickles. The goo can have some dashi and shoyu and sudachi added to freshen it and give an added dimension of taste with texture.
The growing cycle span approximately one year, and should be planted between winter and spring. The traditional methods growing it are: using smaller tubers, top cut of bigger tubers or through cuttings of branches. The first two methods can produce 20 cm long tubers and above. The latter produces smaller tubers 10cm that are usually replanted for the next year. Between 7 and 9 months of replanting nagaimo seedlings, their leaves start to get dry a common fact in plants that grow tubers and that indicates that it’s time to harvest.