Like any and all good science fiction, Space Usagi combines the best parts of a lot of already existing works and welds them together into something unique. It obviously owes a lot to George Lucas, as the first merging of samurai and space, but also for popularizing the more general combination of science fiction and fantasy. Star Wars has been called a "space opera" which is essentially a Lord of the Rings straight fantasy story set in space, but Space Usagi feels like something closer to a "space opera" with all the archetypal elements of any good, classical narrative--a lost love, a wisecracking friend, and arch enemies--only rocketed into space...but not really even?
What is particularly interesting about Space Usagi is that it doesn’t play into the fact that it’s in space at all. It’s almost as if Sakai made up a Usagi Yojimbo conversion chart and simply transferred it into science fiction that way: the Lord’s castle becomes a castle space station, swords become energy swords, and a rhino’s horn is made of metal. When Sakai talks about how Space Usagi came about he says, "I love drawing dinosaurs and I could not draw them in Usagi Yojimbo" (SU FAQ) really downplaying the science part of the comic.
Usagi Yojimbo is a samurai genre comic and being in space doesn’t change its strip style all that much, it just makes it a little more epic. Space Usagi, like regular old Usagi, is concerned about his clan and it's future. The political intrigue, transported to space makes it a bit more serious. It isn't as intense as say the Dune series, but Space Usagi embodies the same strange reality of an ancient civilization in space. Volume Two Issue #1 of Space Usagi seems to pay direct homage to Dune Messiah in it’s opening scene when Usagi is practicing with Kill Globes.
The technology is worked in so seamlessly that when it Sakai uses it for dramatic effect it’s surprising. In one scene, Usagi is listening to the Lord speak to the clan with no real science fiction elements present. Usagi suddenly jumps at the Lord, appearing to slash at him, while loyal retainers all cry out against Usagi. In reality, Usagi had been slicing a ninja with a cloaking device. This would be a cliché (but still awesome) scene in say Lone Wolf and Cub or a Kurosawa movie, but here it adds the additional element of actually surprising the reader. Of course we’re not naïve enough to think Usagi evil, but the actual revealation of a cloaking device is surprising, all the more because we're still training our brain like, "Oh yeah, this is Space Usagi."
Sakai treats death with the same serious tone in Space Usagi as he does in Usagi Yojimbo. Just like in any Samurai genre work, death is treated with a special kind of reverence. Sakai translates that to comic form with a speech bubble with a skull inside suggesting a soul leaving the body. The characters who die, even the minor ones, have awful expressions of pain on their faces. In most comics of science fiction, bit characters are killed off without a second thought--think the new guy in every episode of Star Trek--but Sakai gives them unique faces and intense deaths.
One page shows guards waiting for the attacking ninja to burst through the door. When the ninja burst through they are shot down one by one similar to the opening firefight in Star Wars: A New Hope. Instead of the Rebel troopers quickly falling off screen Sakai has each panel on their actual death. This sequence focuses on one guard as the others around him fall which gives an even greater weight to his death in the last panel of the page.
2009 marks the 25th anniversary of Usagi Yojimo and coming in late November (according to Amazon.com) will come Usagi Yojimbo: The Special Edition. It will collect Volumes 1-7 but nothing of Space Usagi so you might as well go out and just buy it now.