Senzu bean

Senzu beans grow on Korin's tower, a needle of rock so tall that climbing it is itself a training exercise, and the cat who lives at the top hands them out sparingly. A single bean heals any injury short of death, restores all lost energy, and keeps a person fed for ten days. The harvest is slow, so there are never many, and the plot spends a remarkable amount of effort tracking a small cloth pouch.

That scarcity is the point. A healing item with no limit would end tension, so Toriyama built the limit into the supply. Bags get crushed, dropped, eaten by the wrong person, or held by someone standing too far away, and several major fights hinge on a character deciding who deserves the last one. Yajirobe, a swordsman with no interest in heroics, spends much of the series as the delivery service.

The word is sennin plus mame: hermit bean. Sennin are the mountain immortals of Chinese and Japanese folklore, which fits a setting stitched together from Journey to the West, kung fu films and science fiction without apology. Korin, who grows them, is a talking cat several centuries old, so the folklore is not exactly buried.