I've just come back from Jump Festa's Sunday and have run through the Megatheater twice.

The Versus and Agito trailers are the same as the ones that were shown at TGS, I do believe.

The FFXIII trailers (there were two separate trailers shown) had little repeat footage from previous trailers. Please keep in mind, the following is just from the notes I took, and isn't necessarily any more accurate other accounts.

Open the full article for my account. It got really long.

As for the new characters..

I would not call the big new male character's hairstyle an afro, but his hair does look like somebody put a tube over his head and then his scalp exploded, permanently frying his hair up in fine DBZ fashion. It's not long and ridiculously spiky, though. Just... exploded. His hair is VERY orange, and he either has it shaved into thin zig zag shave patterns on the sides of his head or he has a lot of tiny zig zagging braids there. He appears to be wearing a frayed or fur trimmed blue vest and is pretty clearly black. He is wearing off-white to khaki colored long shorts with simple gold patterns on them. He also has a silver necklace with a rectangular, flat silver pendant, wide sides horizontal. He's present mostly in the prison break scenes, helping Snow and the other new male and female characters, although he is the only character I was able to identify for sure on the train with Lightning before she broke out.

As for the younger new male, the first thing that came to my mind upon seeing him was Gippal, probably because of his blond hair and main colors pink and black outfit. He wears goggle-like headgear on his forehead. He does not look 'shota' to me, but he does look young compared to Lightning, Snow and big black new dude. He is blond. He looks to be older than pigtails girl by a couple years. He does talk with an affect. For people who know some Japanese, he tacks 'sska' onto the end of 'ja nai ka' questions to make 'ja nai sska' and 'ja nai ssu'. I don't know exactly the real life implications of the affect, whether its regional, age or culture, but it does exist in real Japanese speech. He seems to often have complaints about situations and courses of action, but help out regardless.

New female character reminds me of Yuffie a little, but her hair is at least shoulder length and appears to be tied back. She does not appear to be very patient. She has a purplish butterfly tattoo visible on her shoulder from the back. I think it's her right shoulder. Her outfit's colors are yellow, white and purple. She is wearing a very short, ruffled layered yellow skirt. She shows considerable amounts of skin compared to Lightning and Vanille. She's also wearing something like knee high fishnet socks. I believe she is shown using a gun.

As for what's happening in the actual trailer, there seems to be two separate parts being told at the same time.

First, there is Lightning rescuing Oerba Dia Vanille on a train with the three new characters and Snow. This scene takes place in the very green colored area with all the train tracks suspended in the air, visible in this image.

I'm not sure about the trailers' order of shown events, as both covered similar events while including different scenes, but the story follows this way..

Lightning and the new black character are on the prisoners' train, dressed in the same white outfits we have seen Oerba Dia Vanille wear when she is captured. They are sitting with several other prisoners. All of them are restrained by some kind of force from the wrist areas of the clothes they are wearing. They talk quietly and briefly to each other, and suddenly the train hits what appears to be some kind of force field barricade set up on its tracks, and begins to run out of control. Lightning jumps out to attack and crushes a remote control-like device with her foot, releasing all the prisoners from their hand bindings. Lightning waves her hand past her hip and begins to generate what looks like an electrical field around herself but appears to be connected to her gravity based abilities.

The large dragon-like flying beasts we have seen before attack the out of control train, seemingly in an attempt to stop Lightning from hijacking it. She shoots at them from the train with a large bazooka-like gun. Eventually they knock the train off its tracks.

The fighting ends up outside, where all the other new characters plus Snow join in. Snow breaks a speaker that seems to be droning out commands from the Holy Government in his entrance scene. Lightning and company have a lot of help in the form of what appears to be a small rebel force, armed with what appear to be standard, bullet-firing guns of fair power. Some of the train rails have been destroyed by the fighting, and the rebels assisting Lightning and company are entrenched in the rubble.

The people who escaped the train when Lightning broke out want to help them fight, and eventually Snow consents to letting them figh to. Among the escapees is Oerba Dia Vanille, who Snow gives a gun to. She takes it, pretends to aim it at an enemy, and says "Bang!"

The fighting seems to get worse, and a heavily armored enemy airship arrives. It blows away a good portion of the resisting fighters with one cannon blast, and Snow is knocked off the train rail while attempting to rescue another fighter and falls from view.

The scene changes to Lightning on a platform with a character who does not appear to be a main playable character by lack of remarkable clothing (His name is possibly Sazzu by the menus). The other character is a male in very plain clothing, although he appears to follow her around for some time as she moves and fights, possibly a guide character.

Lots of fight scenes are strung together, seemingly more for the purpose of showing off the battle menues than carrying the story forward, as eventually it breaks off to the second main storyline focus area: Lightning, Snow and Vanille in the frozen-looking lake area.

There are scenes of them fighting both monsters and soldiers there, and at one point Snow summons Shiva and uses her in battle to attack. Among his menus when using Shiva are attacks called "Diamond Dust" and "Engine". The attack he performs causes damage in many separate increments. In a scene we've seen in magazine scans, Vanille mentions she has seen "that" before, she thinks, although what "it" is is unclear.

Depending on which trailer you're watching, a dialogue about someone named Sera plays either over a scene near the battle at the train tracks area or in lip synch between Lightning and Snow in the frozen lake area, where Snow mentions Sera and Lightning becomes angry at him for not saving Sera, claiming it was his fault that whatever happened to her happened. Snow seems to believe that he can still save her, but Lightning thinks nothing can be done about it anymore. She hits him twice, and both appear to be near tears. He stops her with something he says about what he thinks he can do. (I believe she asks "What is it you think you can do, huh?" in regards to how to save Sera and he replies "Anything!")The blue golem-like creatures are present during some of the voice over conversation. It seems they are somehow connected to what happened to Sera. (Sorry, I'm fairly unsure about the goings on outside the train fighting scenes).

Throughout the train section of the trailers, many, many charactes are shown, most of whom appear to be rebel fighters and escapees from the train, but I've only described in detail the ones who have been seen in gameplay combat or who have unique clothing.

At some point in time (it's shown at the beginning of a trailer, but I can't pin it down chronologically), Vanille is shown standing outside in her white hooded outfit in the green-lit train area, and she mentions the "beginning of the end of the world."

The large green creature/statue like object in the first linked image also features quite prominently in the trailer, but I'm not sure what it is or what it means. In the version where talk of Sera is dubbed over the train scenes, it appears quite often while the conversation plays.