Welcome to Mekton, the RPG that simulates mecha anime. For starters, I'd like to point out that it generally works best with Real Robot stuff, like Gundam, Macross, Frontmission, etc. But first, let's learn how mecha anime works.
-BEGIN LESSON-
1. Real or Super?
Real Robots generally use realistic science and technology for its robots. They tend to be a bit more fragile and reliant on the skill of their pilots. And by "a bit" I mean "most side character pilots will not survive the series". These mechs are found in most of the Gundam franchise, along with Macross, Armored Trooper Votoms, Frontmission, Armored Core, Battletech, and similar works.
Super Robots are usually much larger than Real Robots, with powerful, over-the-top attacks. But they're also much slower, and their pilots aren't often all that skilled, mostly fighting with their MANLY SPIRIT or something like that. The most obvious Super Robots are Mazinger Z (and related series), Getter Robo, Daitarn 3, Gaogaigar, Raideen, and works of that nature.
There are a number of series that blur the line between Real and Super, such as Neon Genesis Evangelion, or Masou Kishin (one of Banpresto's in-house continuities, made specially for the Super Robot Wars series of games). Generally, these mechs are pretty tough and powerful, but also pretty quick, but not too much either way. Compared to the classic Gundams, the Gundams found in Gundam Wing are like this.
2. Setting the mood.
The mood of a mecha anime is far more important than the robots that inhabit it. This determines how the story plays out. This five-point scale should serve to elaborate:
-1: Yoshiyuki Tomino.
This is about as sad as you can get. Character death will be common and often pointless. The ending may kill off the few survivors along with most of the galaxy, end with the heroes failing in a huge way (such as failing to prevent a colony drop), or have the protagonist get Mind Raped by the dying bad guy and be left in a near-comatose state for several months. Basically, this sort of series happens when the director is suffering from clinical depression. Named for the man responsible for like 90% of works in this section, such as Victory Gundam, Space Runaway Ideon, Zambot 3, Gundam Z, and Gundam 0083. Betterman is another rare Super Robot example down here (the others mentioned being Ideon and Zambot 3).
-2: Not too sad, but far from happy.
A fair number of people will die in this show. If a main character dies, it will be a suitably major event, usually followed by someone taking a level in badass. Support characters, not so much. The ending will be bittersweet, the protagonist's survival is not guaranteed. Neon Genesis Evangelion is at the low end of this section. Tengen Toppa Gurren Lagann's second season is at the high end. Code Geass, Martian Successor Nadesico, and Macross Plus are probably the best examples. Typically, shows of this tone and lower feature strong "war is hell" messages.
-3: Average tone.
The main cast can expect a reasonable amount of plot armor, and supporting characters will die good deaths. A main character dying is a huge deal. The ending will be happy, for the most part. Gundam Wing manages this, and is one of the few Gundam series to rise above 2. Rebuild of Evangelion is also here, as is Voltes V. Depending on the exact sub-series, Mazinger and Getter Robo could wind up here (both are parts of long-running franchises, you see). "War is hell" is a common sentiment at this level, too, but far from universal. Big O's weird ending leaves it down here, too.
-4: Optimistic.
The supporting cast is all but immortal, but you can expect a main character to bite it in a most dramatic fashion. The first season of Gurren Lagann is here, as is King of Braves Gaogaigar and G Gundam (Gundam X is a good Real Robot example here). In fact, this is where most Super Robot series end up. There will be a definitive happy ending, Gaogaigar's being the most bittersweet. At this point, the bad guys are pretty much always monsters, and the message generally shifts from "war is hell" to "always have courage and fight for your dreams" or similar morals.
-5: Everybody lives.
Aside from a few minor characters, mostly villains, everyone will survive this and it will be mostly very happy throughout (though not without drama). Turn A Gundam pulls this off (and was directed by a reformed Yoshiyuki Tomino), as does Combat Mecha Xabungle. This is actually a fairly uncommon tone for a series, even the most optimistic Super Robot show will kill off a few people and have some really dramatic moments. This tone is nice for a more lighthearted sort of series.
3. Military or civilian?
Mecha anime generally has two categories. One is the type where the hero is just some kid who found a robot in, like, a lab or something, then goes and saves the day, usually used for Super Robot shows. The other has the hero as part of a military unit, following protocol, usually piloting some sort of Super Prototype or Ace Custom Real Robot.
-END LESSON-
Well, here's the first major thing about Mekton, is deciding how the game's going to be. Now, to keep things simple, we will assume that all Real Robot pilots are military (although "random teen who accidentally wound up piloting a cool robot for the military" is a totally valid character type within that set). Super Robot pilots can be civilians who either found or was "chosen" by a Super Robot, or they can be military test pilots, doing field runs with a special Super Robot prototype or something. Those are all individual choices. The big group choice is the tone of the game. Simply pick one of the five levels. Personally, I'd recommend between 2 and 4. 1 gets really dark, while 5 can get boring at points.
Once everyone has decided on what type of robot you want to pilot, the affiliation of your pilot, and the tone of the game, I'll run mech and pilot creation in more detail with each of you individually. If there's a specific work you'd like to emulate, that's a good start, but I can always assist with my extensive knowledge of both Super and Real Robots, for those unsure of what to do. But, don't think the robots are the only important thing, the best mecha anime are known for having interesting characters, as well, so be sure to give some thought to your pilot's characterization and personal skills (since there are gameplay segments in which you aren't inside your mechs). Specifically, determine your pilot's age (min. 16) and their level of education.