Junior is heir to the throne of Romania, which is bad news for him. The renegade Face and his Sexadolls are planning to kill the entire royal family and take over the country. Fortunately Junior has his own mechanical allies: Lime, Cherry and Bloodberry.
Saber Marionette R is fairly disposable, to be honest. It helps to have watched the other Saber Marionette series (J, J Again and J to X), but even if you already know the characters there's not much connection. Fans have tried to fit everything into a common continuity because fans are like that, but frankly the attempt's pretty ridiculous. The only way to reconcile R with the rest of the franchise is to assume that everyone's unrelated to the regular versions and that any similarity of names or personalities is purely coincidental. However even that's pretty silly. The show's basically a dry run. Trying to set it either before or after the main continuity will just hurt your brain. The character designs, personalities, backstory and SF environment are all different.
Even the production staff mostly didn't stay. The scriptwriter and a producer were used on the subsequent series, but that's it. However interestingly the voice actors all stayed, whether playing ostensibly the same characters (Lime, Cherry and Bloodberry) or different ones that are nevertheless fulfilling the same plot functions. Junior is a prototype Otaru and so they're both played by Yuka Imai. It's even true of the villains. Hikaru Midorikawa plays the evil usurpers Face/Faust and his sexy robotic sidekicks are played by Kikuko Inoue (Brid/Panther), Urara Takano (Edge/Tiger) and Yuko Mizutani (Kyanny/Luchs). Even one of the minor players, Kenichi Ogata as "old guy" in episode two of R, went on to the important role of Ieyasu in J.
There's thus a cosy familiarity about R. The hero, the villain and their respective robot sidekicks are all played by the same voice actors in the Japanese version. Don't know about the English one. What holds it together and lets you pretend there's some kind of connection is: (a) the world, up to a point, and (b) Lime.
The world isn't the same, but it's along similar lines. If you haven't seen any Saber Marionette shows then this might be one of the OVA's most interesting features. It's detailed and well thought out, and instead of getting the background in an infodump you have to piece it together from clues and throwaway references. As before there are clones, plasma rain, etc. However the social side is less distinctive. It's not a homosexual male-only society. Instead there appear to be human women, while the Saber Marionettes have become correspondingly less feminine and more robotic.
There's also a difference in tone. Saber Marionette J was a feel-good TV series, but this OVA series gets quite dark. There's blood, violence and death, some of it imaginatively messy. Furthermore, having only three episodes to unfold in, the plot doesn't mess around. Not everyone survives. The action sequences are awesome, with combatants who can toss around tanks like tin cans, but they can also get brutal. Even the setting is relatively downbeat, with a weight of future history and an air of decay.
Of course we're really watching for Lime, Cherry and Bloodberry. (Junior is a plot token rather than a person, inoffensively likeable but with no distinguishing features at all.) Unfortunately two of the three central Saber Marionettes are unrecognisable. The character designs are completely different, being much more bland and generic, but that's no big deal. More importantly Cherry's degenerated into a harem show bimbo, with her maternal role oddly going to Bloodberry. Instead of being a four-man team, it's a three-man one with Bloodberry only showing later as a sort of Obi-Wan Kenobi. However for me the heart of the show was always Lime and she seems to have sprung into being fully formed. Voiced by the ever-wonderful Megumi Hayashibara, she's unstoppable, hopelessly naive and often very funny. She simply doesn't understand why the bad guys are bad and she'll never stop trying to protect her master. I love Lime.
Saber Marionette R isn't a bad action show, but it's inherently limited by its three episode format. I enjoyed it and even found it moving, but that's mostly because I already knew the characters. There's also stupid harem nonsense in episode one with Lime vs. Cherry... will you laugh or cringe? Probably both. However that soon takes a back seat as Face and his Sexadolls start tearing apart Romania to get at our heroes. There's violence and sacrifice. In the end this story gets emotional. I'd recommend this OVA, but watch Saber Marionette J and its sequels first.