The story is about the Samurai Code of honor, and not letting anger get the better of you.
Here is an introduction from Wikipedia:
"the revenge of the Forty-seven Ronin took place in Japan at the start of the eighteenth century. The tale has been described by one noted Japanese scholar as the country's "national legend." It recounts the most famous case involving the samurai code of honor, bushidō.
The story tells of a group of samurai who were left leaderless (became ronin) after their daimyo (feudal lord) was forced to commit seppuku (ritual suicide) for assaulting a court official named Kira Yoshinaka, whose title was Kōzukeno suke. The ronin avenged their master's honor after patiently waiting and planning for over a year to kill Kira. In turn, the ronin were themselves forced to commit seppuku — as they had known they would be — for committing the crime of murder. "