Here's Blizzard's description of it:
'Dragons' explores the history of conflict between the scions of the Shimada clan: Hanzo and Genji. In this episode, we follow Hanzo as he returns to the siblings' family home in Hanamura once again to seek redemption . . . only this time, he finds himself confronted by the ghosts of the past.
Or, in short, Hanzo and Genji have some wholesome family fun in the form of a life-or-death brawl. They might wield a blade and a bow, but the deadliest weapon of all is emotions.
Source Filmmaker animator Krunkidile predicted the whole thing to a tee before Blizzard ever posted it. If you want to laugh, watch his version: