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.