A boy who lives in a small country in the frontier of the Western Continent. Positive and perserverent, he has a strong sense of justice. Crossing the barrier of "man and Zoid", he connects with all his companions equally. He meets Liger Zero, and his fate changes completely.
Allstar's rival, and a boy soldier of the Empire Army. His late father was also a serviceman, and he's rather elitist.
A girl living in the lost underground world. She's interested in Allstar and the Liger Zero, which looks like the "legendary silver beast machine god".
Party's grandfather. He enshrined the silver beast machine god statues the underground people worshipped, and now passes on the legend.
Originally a Republic scientist. As a pacifist, he experienced doubts about hunting out Zoids for combat and retired. He was living on the frontier, but discovered a liger near death.
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Also, game-original Zoids make their appearance!! After the story ends, something awakens behind four doors.
[The original Zoids are New Tiger, Gojulas 3, and Redler Mk.II, and the latter two bear a good amount of resemblance to some pieces of concept art. The Redler, in particular, was codenamed "Shooting Star".]
Revived by Bluejem after nearly dying in a fight with a Gator (hey, they're scary in this game), it attaches itself to Allstar like a big feline puppy when he stands up for it and Bluejem, saving his life and accepting him as a pilot...and then they fall in a hole and into another world entirely. The Zero occasionally chimes in with "Gau!" and "Grr!" noises as the plot progresses, and at one point roars when it can sense the Panzer armor under the water, much like Lassie with Timmy.
While very much a kids' action series hero, Allstar's also very much a boy: excited by things like mecha and adventure, and slightly scared by things like girls who pop out of a bush and drag him off rambling about legends. He spends a lot of the game looking confused and being amazed by his being thrown into all this, but remains refreshingly humble after all his stubborn heroics. In fact, he often stammers when embarrassed, and his reaction to being proclaimed the underground world's savior is to run off and hide—he was just doing what he thought was right, what's all the fuss?
He's also not as oblivious as most of his kind. Despite flailing the first time Party glomp-kisses him (cooties!), by the end of the game he's not that surprised she's staying or that she admits to liking him. It helps they're both more interested in adventuring than anything sappy.
Solid starts out a rather unpleasant young sergeant...or as Allstar introduces him, "an uptight inflexible blockhead". He wants the Zero but bad to drag back to the Empire, and brushes Allstar off as a naive little kid who makes friends too easily. Even when the BF takes down the Super Geno and Allstar helps out (Party also offers to "kiss it better"), he just runs off again, scoffing at this legendary Zoid thing. Eventually, he reappears to offer a truce in the name of getting back home.
Unlike some unlikely allies, Solid both stays something of a dick and keeps his word without any double-crossing. He even watches the Liger for Allstar while he's Panzer-hunting, despite teasing him that he might take it (and Allstar teasing right back that someone as prideful as Solid wouldn't steal). Being a man of duty, he makes a curt goodbye once they make it to the surface, saying the next time they meet they'll be enemies. He leaves the Super Geno Saurer behind, though, so he may have enjoyed the crazy more than he'd admit.
Party is...well, she's Party, as Allstar finds out from her talking in third person when she drags him off to see her grandfather. The best description otherwise would be hyperactively cheerful (or perhaps genki), combined with curiosity and a habit of calling things cool or awesome—often with added ♥. Her idea of awesome is usually Allstar and/or the Liger Zero, but also includes explosions and Solid's rope-throwing abilities.
Decidedly unshy of expressing her thoughts and feelings, Party stubbornly follows and glomps Allstar on more than one occasion, then flat out tells him she likes him when the end doom's past. Twice, because they're interrupted the first time. Happy to have found a friend and a whole new world to explore, she stays on the surface with him.
Village Chief (aka Grandpa)
Being the elder, Party's grandpa knows lots about the whole "silver beast machine god" legend and what went down at Hope Tower. He thus spends most of the game sending Allstar and company on their quests and explanining bits of plots that need explaining. He seems to be in charge of raising Party, being as her parents don't show up, and he's the one who lets her go with Allstar when she wants to tag along...both on his quest and back to the surface.
Bluejem only really appears in the beginning of the game to save the Zero, but is a nice sort of chap, more into Zoids for science than battle. He was apparently involved in the Zero's modding (from its wild state?), and retired to the frontier and a nice peaceful life after getting sick of the whole Zoids for war buisness. Judging by his snapping at Solid's offer to join his side, he has no real love for the Empire or Republic in a military sense.