Chaz is a 16 year old apprentice hunter serving under Alys in the town of Aiedo on Motavia. The mission to investigate the goings on at the Academy of Motavia is his first. While he begins the story as Alys' sidekick he eventually becomes the main protagonist of the story. While good-hearted and generally idealistic, he has quite a temper.
Can't Drop the Hero: The only character who remains in the party from the beginning of the game to the end.
Kleptomaniac Hero: Averted; if you attempt to make him search drawers/cabinets in peoples' homes, he'll remark that it's not very nice to look through peoples' belongings without their permission. He'll look in the cabinets in Inns, or in houses if he doesn't have to open a closed container, though. Apparently, Motavians are into orange soda, and one of the Inns on Motavia provides Game Gears for its guests. (And possibly hookers.)
Magic Knight: Eventually gets both the most powerful physical attacks and the most powerful offensive magic in the game.
Sensitive Guy and Manly Man: Pretty much everything Chaz does is based on his feelings, and although he's constantly bewildered (and sometimes frightened) by the technology popping up all over the place, he understands people better than anyone else in the party...while Rune is an insensitive jerk.
Refusal of the Call: On Rykros, he initially flat our refuses to go along with the Great Light's plan in maintaining the seal that is the Algo star system; he reconsiders when he thinks of the people of Algo he'd be fighting to save.
A veteran hunter, Alys is Chaz' mentor and surrogate parent. She's the main character of the early part of the game, but this changes after she is incapacitated by, and later dies due to, an attack from Zio, the first of the game's villains. Brash and supremely confident, Alys is not above threatening people for money and/or information if it makes her job easier.
Berserk Button: Don't talk about her measurements while she's in earshot.
Crutch Character: Initially, she's far more powerful than anyone else on your team, but she gains levels, stat increases, and abilities far more slowly than everyone else does, so they quickly catch up.
Decoy Protagonist: You'd be forgiven for thinking she's the main character, given that her name and appearance are so similar to those of the heroine of the first game in the series. She's not, though.
Heroic Sacrifice: She saves Chaz's life by leaping in front of Zio's "Black Wave" attack, at the cost of her own.
Does Not Like Men: Excepting Chaz, her trainee, Rune, her fellow student and childhood friend, and the bartender at the Guild, she doesn't seem to think very highly of dudes in general. But that may be because she's the top hunter in a highly competitive, male-dominated profession, and most of the men she knows are either putting her down, trying to suck up to her to get an advantage, or hitting on her.
Killed Off for Real: Well before it happened to a certain flower girl, hence she's one of the first example of a major character being killed off in a JRPG.
Red Baron: Alys "The Eight-Stroke Warrior" (or, more accurately translated, "Rip-Their-Guts-Out Lyla").
A young scholar at the Motavian Academy, Hahn is the one who hires Alys and Chaz to look into the monster infestation in the Academy basement. When it turns out there's more to the situation than meets the eye, he tags along with Alys and Chaz to try to get to the bottom of the mystery.
The Blacksmith: It's his family's business; toward the end of the game he forges a powerful dagger and shield which only he can equip.
Took a Level in Badass: Before the final battle, he claims to have been secretly training. He ends up having offensive magic second in power only to Rune, plus a few more instant death techniques (including one that targets all enemies).
An old friend of Alys', Rune is a snarky, blue-haired wizard who possesses a gift rarely seen in Algo these days - the ability to perform true magic. Initially, he only accompanies the party briefly, but after Alys' incapacitation he joins up for good.
Expy: Of Lutz from Phantasy Star. Justified in that he actually is Lutz, reincarnated.
Jerkass: During his first stint in the party, he's quite rude and condescending to Chaz.
Linear Warriors, Quadratic Wizards: Inverted; during his first stint in the party, Rune is of a much higher level than your other party members, and can pretty much nuke any enemies you encounter on his own. When he later rejoins, he's still powerful, but not noticeably moreso than the other characters.
Squishy Wizard: The squishiest in the game. However, with the aforementioned Dual Wielding of Silver Shields, he takes surprisingly little damage from magical attacks late in the game. Wren, of all characters, is in worse danger from the final boss' onslaught than is a properly shielded-out Rune.
A native Motavian warrior, Gryz joins the party after they journey to the Motavian village of Tonoe in search of a magical antidote, and tags along afterward in hopes of avenging Zio's attempted genocide against the Motavian people. He hits hard, but is rather slow and has no magical abilities.
Rika is a Numan, a genetically engineered being created in an underground laboratory by the computer Seed. Though she's only a year old, she looks like a young adult woman. She possesses an optimistic, friendly personality, and all the curiosity you'd expect of an intelligent being that's never seen the outside world.
Skilled, but Na´ve: Despite being among the most powerful characters you can get in your party, she's not very worldly, as you might expect of someone who's spent the only year of her life in an underground laboratory.
The Mario: Deals decent melee damage, is a decent healer, takes a reasonable amount of damage and has some useful buffs.
Zettai Ryouiki: Perhaps one of the great-grandmothers of this trope: she wears a black leotard (and heavy-class armor), but she wears thigh-high boots that are pretty standard from the front, but from the back, they just barely reach the hemline of her cape.
One-Winged Angel: Goes through three forms when you fight it; oddly enough it's the last one that's the least monstrous.
Retcon: In previous games in the series, Dark Force was portrayed as the ultimate evil in the Algo solar system. While this is true in a sense, PSIV reveals that it is in fact only a representative of the world's true Big Bad.