Official story and features:
"The story takes place on an unknown planet in the not-too-distant future. On this world, a surge in crime involving dangerous, miniature robotic weapons known as Custom Robos occurs. Those that manipulate the Custom Robos are commonly called "Commanders," and through specialized training, they learn to manipulate the robots' actions through the use of brain waves. One day, the hero and his comrades learn of an incredibly strong robot with autonomous maneuvering capabilities. In their search for a logical explanation regarding the existence of this powerful foe, the hero and his comrades uncover a secret about an event that occurred on this planet several hundred years ago..."
Story from Nintendo site
"- Leap into a mechanized melee! Hone your skills in the single-player role-playing game as you progress through a deep sci-fi storyline.
- Make your own soldier! Customize robots by choosing from more than 200 different parts and weapons, then test their one-of-a-kind abilities against other robots in one of 30 battle arenas.
- See if your custom robot can survive the frantic, chaotic action of a four-player battle royale, two-on-two vs. Battle mode, or Tag-Team battle match!
- Battle it out with three other players on a single screen (rather than split-screen), and enjoy a great multi-player party experience. You can customize your own robot, then test its power in battle arenas against other players' robots."
Features from Nintendo site