What kind of a title, you may be asking, is J9? It's the title of a metafranchise. That is, a "series of series" which are at least nominally connected to each other. Specifically, it's a "trilogy" of series, those series being Braiger, Baxinger, and Sasuraiger. Shockingly, the three series actually have continuity with each other, which is perhaps the only thing that makes them worthy of talking about for any length of time.
Of course, the series are set hundreds of years apart, and thus any continuity between them would merely be "historical." Right?
(Note the robot with the HAL-9000esque head that towers over Braiger yet gets cut in half with one stroke.)
Of course, the thing about history is that it's usually considered to be big, important things happening. And what could be more historical, in this respect, than a failed attempt to turn Jupiter into a second star resulting in its destruction and the reordering of the Solar System?
You read that absolutely right. Some crazy person wanted to turn Jupiter into a star in order to make it and its planets into a new Solar System. Theoretically, this would have resulted in 30+ habitable planets (apparently moons of Jupiter aren't legitimate targets for the superadvanced terraforming technology that they explicitly possess in this series) and thus, er, allowed a huge population boom or something? That this guy would have ruled over, maybe? I dunno.
So the next series, 600 years later, doesn't have Jupiter in it. (It apparently also sees the lowest possible legal neckline as not being a fashion faux pas of any kind.) It does have a squad of people who are called "J9" after the heroic team who kept Jupiter from being destroyed (wait...) (because it apparently was profitable to save Jupiter [wait...]) with their very multicolored robot that formed from their magic motorcycles (there we go).
(Considering that this same studio made Macross (AKA Robotech), where there were humanoid aliens who on an individual basis stood as tall as robots that transformed from fighter jets, it really shouldn't be surprising that the enemy robots were so freaking huge here.)
And then, Sasuraiger, another 200 years later (exactly 200 years, just like the previous series was exactly 600 years after the one that came before it-suspicious) features a train that turns into a robot (or a robot that turns into a train) which according to stuff I have read is sometimes called Batrain (I'm Batrain). The train, of course, is an interstellar spaceship that allows the cast to travel the galaxy, looking for planets where they'll be happier or something-e.g., two of the characters are youngsters looking for a planet that allows underage marriage. WHAT.
There's not much more to say, I think.