Featured: A show that had official porn made of it to fund a second Season.
Battle Century G is built on the idea of having an effects-based universal system for Mecha. That is all well and good, but Macross is very different from Godannar which is very different from the Evangelion. Odds are that if you were to try and run a RPG centered on their worlds with their cast of characters, some (or most) of them will feel out of place. The differences in tone between Godannar's hijinx and Evangelion's drama is so jarring it grades on the Richter magnitude scale. From this we have to conclude that you cannot really make them part of a single unified Genre.
So what is this Mecha Genre then? A lot of Mecha fiction has common elements that, during the translation to a different medium, we can emphasize to make them stick and build the rest of the narrative around. Battle Century G has a distinctive feel to it gained from the way it mixes and matches elements from many different genres into a single cohesive entity.
Collaborative Tone and Mood
A few sidebars tackle some of the issues you could run into when translating giant robot storytelling conventions into Roleplaying Game form. For brevity's sake I will not be discussing the complications, but instead I'll bring to the front how it facilitates things. Starting with issues of Tone and Mood.
For those who don't know, the Tone in fiction is the attitude the writer or narrator is trying to convey about their piece, while Mood is how the reader or audience feel in response to the Tone. A Roleplaying Game about kids who build custom robots that beat each other up in a world tournament that has an upbeat Tone and embraces its zaniness will probably have a Mood like ROBOT FIGHTS ARE AWESOME. On the other hand if the Tone is about children being brainwashed from an early age into piloting actual giant robots when they come of age to die for their country then the Mood will probably be a tad more cynical and grim, even if the plot only goes as far as the teen championships.
Pictured: A gritty drama about glorifying violence and consumerism. Not pictured: My sarcasm.
Tone in Roleplaying Games is usually the GM's work. They have the entirety of the world with all of its NPCs to sell the other Players a Tone. The job of the other Players is to establish a Mood, since the audience surrogates or main characters aren't written by the GM, but the Players. The GM can then take their Mood input and adjust the Tone according to their actions, or reinforce the intended Tone so the PCs will react accordingly and adjust the Mood themselves.
That alone takes care of the big issue about jarring shifts in tone and mood. It is a collaborative process, and everyone gets a say in it, so as long as there is an intent to actually collaborate from all parties involved things are a lot more likely to work out well. You can have lighthearted stories that get much darker sometime in the middle, or with intermittent spots of heavy drama, or just run a rollercoaster of a narrative full of extremes. You have to be careful with extremes of any kind, but this is a medium where the director gets to ask for the audience's consent first, so it usually works out much better.
Genre Themes incorporate the possibilities for doing all of those into a tiny little package that you can take in whatever direction you want. It is at its best when there are shifts from the whimsy of Typecasts to the heroics of Reasons to the tragedy of Banes. It does not have a set Tone or Mood, but you could say that it can fluctuate very well between a variety of them.
A whole lot of shows with giant robots feature a cast of characters that is there to support the leads not just in a narrative sense, but in a fictional sense. There is this big organization staffed with mechanics who keep the robots functional, engineers developing their weapons, operators who keep the pilots up to date with information relays, and so forth. Everyone also has a common enemy they are fighting against like the Mecha Demon Legions from Hell, or the Space Nazi Empire, or just Kaijus From Another Dimension.
Most of the time this is just a handy way to to populate a series with a cast of minor characters who are relevant every once in a while and to let the main cast provide different perspectives on the same conflict. Many shows do away with the idea altogether and have the main characters as loners taking care of jobs without any immediately obvious connection to them. And they are pretty good shows!
But in Battle Century G assumes you are going to have a cast facilitating things out for the PCs as a single force. You could have a story about wanderers with robots looking for fame and fortune but the game expects you to have a recurring cast and for all the PCs to have a clear shared goal that keeps them working together.
This is a very big contrast to how most Roleplaying Games work. In the grand majority of them the PCs are wanderers looking for adventure and never staying in one place, the genre is like Pulp mixed with a Western. The second wave of massive Roleplaying Games did expect you to have established setpieces and a recurring cast to keep coming back to, but it also encouraged the PCs to split up among various factions and to be at odds with each other. These games are more about political intrigue and drama than combat, so it works for them. But they're still pretty different from Battle Century G's defaults.
Just in case you couldn't tell, this is who I am talking about.
Other games have "Alignment Systems" where characters who associate themselves with a similar moral values stick together, but if they don't want to they don't have to. That makes having conflict between them difficult, because they can just cut off communications between each other entirely. BCG wants everyone to be distinctively on the same side of the conflict. Even if they don't like each other, they have to work together if they want to win. They can have differences in how to resolve the conflict, or what to do after it is over, but the PCs are meant to be an unified force and so are the NPCs.
The unity of the group around a common faction is a subtle but important element of what makes the game work. It permeates everything from the attitudes of NPCs to why characters who hate each other might want to try and find common ground. The Faction that the PCs belong to is in many ways the avatar of Tone, it influences the Mood and the Mood of the PCs influences it in turn.
You could say that BCG's Genre is one of Faction-Based Action/Drama. You have a common goal, giant robots to fight with, and big heroes who trump big challenges. I'd like to go more in depth about this later, regarding which series it represents very well and which ones take more effort.