A power-up found in
Mega Man for the
Nintendo Entertainment System. Only one exists in the game (the word means "the one and only" in Japanese), and it's found in the final
Dr. Wily level above a bed of spikes. When collected it refills
Mega Man's life and weapon meters. It also has a point value of 100,000.
The item also shows up again in Mega Man 8 performing the same function and in Rockman Battle and Chase it provides temporary invincibility.
Rumor has it that the Yashichi was in every Capcom game of the late 1980s, although I cannot find information to confirm or deny this.