Nanki-Poo is a character from the comic opera "The Mikado," composed by Arthur Sullivan with a libretto by W. S. Gilbert. He is the son of the Mikado, the emperor of Japan, and disguises himself as a wandering minstrel to escape his responsibilities and pursue his love for Yum-Yum. In the story, Nanki-Poo is in love with Yum-Yum, who is engaged to another man, Ko-Ko. The plot unfolds with themes of love, mistaken identities, and social satire, all set against the backdrop of a fictionalized version of Japan. Nanki-Poo's character adds humor and charm to the opera.