"In the 21st century, the war of the Transformers has shifted to space, and seemed for a while that peace had returned to Earth. However, during that time the Autobots had been working together with Earth scientist Professor Chase to develop a new combination system. With it, Autobots would use Power Core Combination to combine themselves with 4 Drones. The Autobot warriors chosen for the process became part of the group known as the Master Class. At the same time, a covert counter-team of Decepticons with the same capability, "Master Chaos," was formed."
The story told on the package backs reflects the atmosphere of the United series, while including characters from earlier Transformers series such as wheelchair-bound genius Chip Chase.
Combatmaster Prime Mode
A Decepticon strategic commander who has been active since the early stages of the war, Combat Master combines with 4 military vehicles. The weapons that line his body provide devastating firepower. In the story, his drones were stolen from the Autobot Chopper Master, who they were originally developed for.
Drones: Morser Drone, Panzer Drone, Kanonier Drone, Spaher Drone
Jetmaster Prime Mode
The Autobot spy Jetmaster combines with 4 jet and helicopter Drones. Jetmaster was the first Autobot to successfully achieve Power Core Combination. The character features details referencing earlier Transformers series, such as that the data for his drones was gathered from the Aerialbots, and that he was born on Planet Z.
Drones: Zone Drone, Feminia Drone, Micro Drone, Tenth Drone
Aerial Warrior Choppermaster
Polar Commander Rollermaster
Hopefully the story will comvince some people to buy PCC when they're out next month.
EDIT: Further elaboration from Hydra:
Now that this preview is out there, it's probably safe for me to explain a few things about this, but...
United EX was written to be part of the Japanese G1 cartoon continuity, as it explicitly takes place near the end of G1. It's not linked to the one-shot Generations manga. This becomes very clear as the story progresses.
My understanding of the United toyline itself is that it doesn't have its own unique continuity (although there are new story elements introduced in it), and basically just depicts various moments of Transformers history, primarily from the Japanese cartoon continuity. Granted, some of the toy forms differ from their G1 cartoon depictions, but that was true for G1 itself...
Some of the naming, such as Master Class and Master Chaos, and obviously individual guys like Grimmaster and Racemaster, is admittedly a little clunky in English, as it was intended for the Japanese market. The product names were determined already, and the Master... was my effort to explain why a whole slew of Transformers might all be called ****Master.
The basic premise is that during a short period of peace on Earth, when most of the fighting occurred offworld, the Autobots were working together with human military organizations to create a combination technology that could be made useful either in times of peace or war. Because most of the more experienced Autobots are away from Earth, they needed to design the system to provide the wearer with considerable power, since the Decepticons gathering on Earth once again might otherwise be a disaster for the remaining Autobot forces. Thus, Prime Mode: a combination form designed to bestow the core with might rivaling that of the Autobots' great leader.
The codename for this group was "Master Class," a gathering of young Autobot professionals in various fields such as recon, defense, construction, etc. who intended to use their skills for the benefit of Earth. Because of the classified nature of the project, each received their own codename, "Masters" with their actual identity not made public. Some joined the team to gain experience, some to prove themselves, and some to make up for past misdeeds. At the same time, a small group of Decepticons lying dormant on Earth got wind of this and formed a counter-group they called "Master Chaos," seeking to seize the drones and take control of Earth in Megatron's absence.
I'll be very excited to see if Japanese fans enjoy the story when the releases begin next month.