The short film format is perhaps the most difficult. To create a world, convey a story and to leave the user wanting more while at the same time giving them a sense of the story being resolved is a difficult proposition in 90 minutes, much less 8 minutes (the run time of Muramasa.) That is precisely what Muramasa does.
There isn't much story you can fit in 8 minutes. Fortuneately the samurai genre is well suited to this, there is no need to explain a story as old as time. Motivations are simple for warriors; power. The protagonist, an unnamed samurai, finds a Muramasa katana and takes it up. Those of you familiar with the legend of Muromachi period swordsmith Muramasa Sengo and his demon blades may have some idea of what to expect. The rest of you read this; http://en.wikipedia.org/wiki/Muramasa.
The art in Muramasa may seem a bit rough to some, but resembles traditional wood block prints (木版画, moku hanga.) Though they weren't popularized until the Edo period, there is certainly an abundance of prints from the Muromachi period as it was the first means of mass production, preceding the printing press. By using this wealth of history as his backdrop Osamu Tezuka sends you back in time. There isn't a whole lot of animation in Muramasa, it's almost a picture drama. The style presented is nevertheless very atmospheric, and pretty unique from anything else in anime. My only criticism would be that the concept wasn't extended far enough. Character models don't seem to be based on traditional art and are somewhat bland.
The music immediately sets the tone for the film. Eerie Noh flute and other traditional Japanese instruments pervade the soundtrack. The tone and tempo follows closely with the action and creates a sense of mounting tension and intensity. The traditional music brings together the traditional art and story to create a fully immersive experience.
The film begins with the caption "A man with arms which can kill people like puppets is not aware that he himself has already become a puppet." It explores many themes related to war and mans desire for power. The unnamed samurai undergoes a spiritual, psychological, and physical transformation as he follows the path of the warrior. As he kills more men will he stay true to the path or will he become corrupted by power and the demon blade?
It's probably not apparent from watching, but Muramasa is actually a political metaphor. Tezuka was an outspoken critic of peace through nuclear deterrence, and Muramasa was made around the peak of cold war hysteria. Politics aside, there is no doubt in my mind that this is one of the best short films ever created. It no doubt takes some relevant information of Japanese history and culture to fully enjoy Muramasa, but if you are armed with that knowledge I'm sure you will appreciate this masterpiece.