The Berserker: Turning into the Kaiser Dragon at first turns him into an uncontrollable force that targets allies and enemies alike. There are only two gene combinations that avoid this, the simpler one reduces his stats gained from the transformation so much you might as well not bother and neither one is even hinted at in-game.
Cat Folk: He's a member of the Woren tribe, though very few Woren are actually seen in this game.
Chick Magnet: Several maids in Castle Wyndia are quite taken with Rei.
Crutch Character: In the first part of the Childhood Arc, he's level 5 when Ryu and Teepo are level 1, he gets Extra Turns in almost every fight due to his high speed and he will be capable of killing almost any random encounter by himself and can deal some good damage to bosses. When he reappears in the Adult Arc, he's around Ryu's level and while Ryu's likely more powerful then he is due to his dragon forms, Rei still likely has higher speed. He even lampshades this after you beat the Weretiger, admitting that he knew he could never beat Ryu.
Fragile Speedster: He's always the one to go first unless you cast Speed multiple times on someone and is the most likely to get Extra Turns, and while he can deal some decent damage, he can't take it very well.
Gentleman Thief: He'd never hurt the townfolks as he steals to survive. Although after the timeskip he "jokingly" asks Ryu if he wants to go slaughter the population of McNeil together. He also states, vaguely, that "I wasn't even able to control my own power. All I did was just run around attacking things..."
Knife Nut: He dual wields knives but he only uses one of them when attacking.
Bad Powers, Good People: Teepo agrees with Myria's views about the Brood, and sees their power as something that only causes destruction, war and death. And why he thinks both he and Ryu need to be isolated, to prevent more of that to happen.
Returning to Castle Wyndia and speaking with the people inside, express their favor for Nina's choice of living (even the king, though in his case it's only implied). Sheila really is the only one who disapproves.
Rebellious Princess: She refuses to live in a gilded cage and wants to experience the world, but her mother won't let her. Nina's last words to her mother in the story are that she has to be free to be herself before fleeing the castle.
Glass Cannon: Even early in the game, she can do a ton of damage. Over the course of the game, she does get a little more balanced, though "lots of damage, hope you dodge" still remains her role. This does make her somewhat unreliable, though she still remains useful in many situations.
The Ugly Guy's Hot Daughter: Not exactly, but invoked by Garr to sneak into her home town to return her to her parents without being held suspicious. The guard they fooled to sneak in remarks that her mother must be beautiful.
Winged Humanoid: Much less noticeable due to the race's decrease in power, which leads into...
Wings Do Nothing: The only Nina whose wings grant her no special skills or abilities. It's even hinted they're just accessories and Wyndians don't have wings anymore.
Required Party Member: Any time there's a machine/computer involved in the story, don't forget to bring her with you. The game doesn't force her into your party, though, and often the place you need her is halfway through the dungeon, forcing you to walk out, put her in your party, and walk back. Especially notable in the Factory, where you need her bazooka to blow open a malfunctioning door that blocks your progress. The game gives you zero hints about this.
You can also use Ryu's sword to blow open that same door.
The Atoner: During the second half of the game after realizing that the Brood could have easily killed him and the other dragon slayers in the war if they wanted to. He spends the rest of the game wondering why God had them killed and wants to learn why. Interestingly enough, Ryu and the Brood of Dragnier holds no grudge against him for it.
Big Guy Fatality Syndrome: An unusual take on the trope, in which simply choosing to participate in the final battle turns out to be the heroic sacrifice. The others don't know until it's already too late.
Dragon Slayer: The last one still inhabiting the world. But after losing to Ryu in Angel Tower, he realizes that the Brood would easily crushed the Guardians if they wanted to.
Duel Boss: During the final battle of the Contest of Champions and again in Angel Tower.
Dropping the Bombshell: Ryu's goal of finding his family are completely dashed when Garr spells it out for him that, Balio and Sunder being cutthroat criminals, Rei and Teepo have a slim chance of still being alive. Of course, Garr would be proven wrong later on, but...
Cool Old Guy: He tries to keep an eye on Rei, Teepo and Ryu throughout the Childhood Arc and is genuinely disappointed when they break into his house but forgives them anyway and teaches them the value of honest work.
Gentle Giant: Outside of knocking out and tying up the trio for breaking into his house, he prefers to use words to teach and can give some of the best physical moves in the game as a Master.
Curb-Stomp Battle: Rei really should've thought twice about choosing his hut to ransack.
What the Hell, Hero?: He was so disappointed in Rei and company after they break into McNeil Manor, he didn't tell them outright, and instead had to say it "discreetly" (faking a conversation with a cow so that they could remain hidden).
McNeil and ghost ancestors (Kanzei, Torast, Kassen, Galtel, Doksen)
Bilingual Bonus/Shout-Out Theme Naming: As befits a line of money-grubbing aristocrats, McNeil's ancestors are named after business terms: Kanzei = customs, Torast (Torastu) = trust, Kassen (Kashisen) = "cashes in", Galtel (Karuteru) = cartel, Doksen (Dokusen) = monopoly. Their merged form Amalgam is called "Congermerate" (conglomerate) in the Japanese version.
Jerkass: They're both remorseless killers whose first scene involves burning down the trio's home and trying to murder them, then stabbing Ryu, kidnapping Nina to ransom her for money after manipulating her into freeing them and knocking her out to fight Ryu, brutally assaulting Ryu and taking him and Nina to Gemmel and then chasing them all around the countryside and being smug assholes about it.
Knight of Cerebus: The lighthearted adventures in the Childhood Chapters with Rei and Teepo come to quick end when they show up.
Shout-Out: Stallion's design and trademark technique are one to Ultraman. He even strikes his popular L-pose while using it. For some reason, the references were removed in the PSP remake, with his color changed to brown and his technique renamed.
Shock and Awe: Balio uses Lightning in both of the battles where you fight him.
Would Hurt a Child: Their first appearance is brutally beating up and trying to kill Rei, Teepo and Ryu after burning their house down, then they stab Ryu in the back on the top of Mt. Myrneg to try and kill him. They then kidnap and knock Nina out to beat up Ryu and a little later when they're threatening to kill Nina, a princess from Wyndia to make Ryu surrender, they brutally assault Ryu into unconciousness.
Arranged Marriage: Shadis' father Sinkar wants her to marry a strong sailor, so he's set one up for her with Zig. Beyd isn't too happy about this, and asks the party to train him in combat.
Badass Normal: The badass part depends on the player's way of training him: if one is diligent enough, Beyd can end the battle in 1-2 hits.
Statistically Speaking: You can overtrain him, make so he takes 1 damage from your + 30 level party and defeats Zig in a few rounds, taking no damage in the process. He's still beaten up and bandaged in the next scene.
Took a Level in Badass: Boy howdy. Wimpy bookkeeper turns into master swordsman and Leader of the Porter's Guild.
Training from Hell: One of the best methods to train him is to hit him as hard as possible, which raises his defense.
Crack! Oh My Back!: Every three turns during his Boss Fight, he'll waste a turn with the "Bad Back" skill. You can even learn it from him, though it doesn't do anything.
Dirty Old Man: He will not allow you to undergo his "test" unless you take Nina with you, foreshadowing a Required Party Member scenario note but actually subverting it, as you can switch Nina out for another member after she talks to him. This becomes hilarious when you take Momo to meet him instead and he outright complains that she "doesn't meet his qualifications"—which makes her furious.
Fan Disservice: She wears Godiva Hair during her battle. Except for her default attack, where her guts rupture out to slap someone as her hair flies back.
Gnosticism: The early games hint at it but Breath of Fire III finally confirms that Myria is meant to be some kind of parallel to the Demiurge, as she believes herself to be a divine being despite implications that she isn't standing...implications that she seems to accept at the end.
Our Angels Are Different: She's usually seen assuming the form of a winged woman with light all around her. However, there is a distinct Uncanny Valley effect you realize that her wings are upside down.
Power Source: It is stated the chrysm, the fuel for all machinery on the world, is a medium for Myria to provide the world with her magical energy.
The Scottish Trope: The Urkans (and Guardians) are prohibited from speaking the name of their goddess, or that of her enemy the Brood.
Villainous Breakdown: An unusually humanizing one. When she's defeated, as she is dying she worries about how the world will continue on without her, and calls out to God ("if there is a God") to ask what she should have done instead.
Well-Intentioned Extremist: She's protecting life and the world by sending the technology of Caer Xhan to humanity via the Black Ship in manageable doses, keeping the Desert of Death away from humanity with an ocean barrier, and stopping the Brood from destroying the world with their power. Unfortunately, sending machines to humanity means making humanity dependent on her, keeping the Desert away from the rest of the world prevents humanity and Yggdrasil from colonizing and restoring it, and protecting the world from the Brood means either killing them all or imprisoning them in a false Heaven, regardless of whether or not they've done anything wrong.