The play itself was based off of Heike Monogatari--an epic based on the conflict between the Minamoto and Taira clans in the 1180s. It takes place a few years after the end of that war, and involves Minamoto no Yoshitsune's pursuit of three remnants of the Taira clan, all of them generals that are potential threats to the shogunate.

...There's at least ten characters in the play I can name off the top of my head; the one I mentioned is the protagonist. [The same person he'd literally made a persona of. But he isn't telling her that. :|']