Whilst investigating a sudden mass swarming of insects, researcher Takuya Kai of the Earth Academia meets the mystical Insect Elder Guru. He tells him that the insects sense the invasion of the extra-dimensional Jamahl Empire, and are preparing to fight them. With Guru's help, Takuya and his mentor Professor Mukai develop three Power Armor suits infused with the power of beetles. One suit is entrusted to Takuya, the other two to Daisaku Katagiri and Rei Hayama. They become the B-Fighters, who regularly oppose the schemes of Jamahl and its three generals.
- Takuya Kai/Blue Beet: The Leader; an insect researcher from Earth Academia who is the first to learn of Jamahl's evil schemes.
- Daisaku Katagiri/G-Stag: Big Lancer; a tree doctor who claims to hear the voices of trees.
- Rei Hayama/Reddle: Fragilistic Chick; an animal instructor. She left to do animal research in South America and was replaced by Mai Takatori.
- Insect Elder Guru: The Mentor.
- Kabuto: Essentially, the fourth B-Fighter; Guru's Beetle-armored son who left him to pursue a career as a weapons supplier.
- Emperor Gaohm: The Big Bad
- Jera: The Dark Chick
- Schwartz: The robotic Evil Genius
- General Gigaro: The Brute
- Sorceress Jagul: Another Evil Genius; the Sixth Ranger responsible for Shadow's creation. Actually killed off shortly after, but comes back once every other villain is dead.
- Shadow/Black Beet: Takuya's Evil Twin.
Recurring Metal Hero tropes include:
- By the Power of Grayskull!:
- "Juukou!" ("Heavy Shell!")
- "Jakou!" ("Evil Shell!") for Black Beet.
- Calling Your Attacks: As per the Toku norm, the B-Fighters call out their finishers when they perform them.
- Humongous Mecha: The Beet Machines, a trio of beetle-themed vehicles, and Mega Heracles, a gigantic mechanical Hercules beetle.
- Monster of the Week: The Jamahl have three Armies, who each take turns volunteering one of their kaijin to fight the B-Fighters. Some of the most awesome Kaijin in the Metal Heroes franchise appear in this show.
- Mooks: Jahmal's Jamars.
- Phantom Zone: For the first time in years, we get one in the form of the Gaohm Zone. The fight scenes which take place in it range from slightly weird to flat-out insane. Some parts (such as one instance where G-Stag ends up getting randomly slashed with switchblades on a busy street) are outright bizarre.
Juukou B-Fighter provides examples of the following tropes:
- A.I. Is a Crapshoot: Schwartz goes steadily crazier as the show continues. After losing his body he goes completely Ax-Crazy and rampages until he's stopped by the B-Fighters.
- All Your Powers Combined: Jagul absorbs the powers of various monsters to assume her One-Winged Angel form.
- Back from the Dead: In the epilogue, which doubles as a crossover with the two previous Metal Heroes shows, Jagul revives Bill Goldy and Queen, along with several other villains from all three series, and later absorbs them into her One-Winged Angel form.
- Bad Boss: Gaohm's methods for completing the Jamahl Hole end up costing Gigaro and Schwartz their lives. He also kills Jera for seeing his true form.
- Berserk Button: Do NOT attempt to cut down a tree when Daisaku is nearby.
- Chekhov's Gunman: In episode 52, The heroes prevent Gigaros resurrection as part of Jaguls scheme. This ends up leaving the Destruction God with a glaring hole on her body to exploit.
- Crossover: The two-parter final episodes featured Blue SWAT and Janperson aiding our heroes.
- Designated Girl Fight: Averted. When the three Jamahl Army Commanders are sent out to fight the B-Fighters in episode 18, Blue Beet fights Jera while Reddle takes on the Evil Genius Schwartz.
- Dragged Off to Hell: Jagul gets this from Bill Goldy in the finale.
- Dragon Their Feet: Jagul, who was previously a two episode minion of Gaohm, comes back in the finale to serve as the Post-Final Boss.
- Drop the Hammer: The motif of episode three's monster, Hammer Kong.
- Everything's Better with Spinning: The B-Fighters' weapons all spin when activated.
- Grand Finale: With shades of Fully Absorbed Finale, as Janperson and Gun Gibson, plus the Blue SWAT team, all assist the B-Fighters in the epilogue.
- Greater-Scope Paragon: Saint Papilia, a literal Butterfly of Death and Rebirth who appears every time the Earth is destroyed to restore life to the planet. It is the goal of Gaohm and the Jamahl Empire to harness her power to give themselves immortality.
- Green Aesop: Although it decreases over time, the show often focused on damage being done to the environment, with most of the B-Fighter's weapons and equipment being infused with insect powers.
- Japanese Beetle Brothers: Blue Beet and G-Stag are a Type A.
- Killer Robot: The Combat-Mecha Army, led by Schwartz, is full of evil robots built to cause as much damage as possible.
- The Man Behind the Curtain: The Gaohm we see for most of the series is actually a dummy, with the true Gaohm being an entity contained in a tank full of liquid.
- Mid-Season Upgrade: Blue Beet's Beet Ingram gun, which allows him to transform into Super Blue Beet.
- Noble Demon: Black Beet.
- No Ontological Inertia: Actually averted for once. Even after Gaohm is destroyed, the Jamahl Hole doesn't disappear right away. It takes G-Stag and Reddle using their Beet Machines to shoot it to finally do away with it.
- One-Winged Angel: Jagul turns into her "Destruction-God" form, fusing herself with various destroyed monsters, as well as a few villains from Janperson and Blue SWAT; it takes Super Blue Beet's Beet Ingram, Hyper Shou's DrumGunner, and Janperson's Flash Cannon, and being Dragged Off to Hell by Bill Goldy to defeat her.
- Omnicidal Maniac: Gaohm plans to use the Jamahl Hole to destroy the Earth in order to summon Saint Papilia so he can capture her to gain immortality.
- Out of the Inferno: Pulled by the B-Fighters in episode three, when walking out of a destroyed building.
- Post-Final Boss: Actually has two. After the B-Fighters destroy Gaohm, Takuya has one last one-on-one duel with Black Beet and destroys him for good. Then, in the two-part epilogue, the B-Fighters team up with Janperson, Gun Gibson and Blue SWAT to beat down Jagul, who inexplicably survived the Jamahl's destruction.
- Powered Armor: The B-Fighters' Insect Armor.
- Power Trio: Blue Beet, G-Stag and Reddle of course.
- Put on a Bus: Rei leaves the show in between episodes 21 and 22 to go help out wildlife in South America.note
- Super Soldier: The Toku version since Metalder.
- Super Strength: One of the powers given to the B-Fighters by their armor.
- Synchronization: Whenever Shadow hurts Takuya, or vice-versa, they each feel the pain.
- Thanatos Gambit: In order to truly get a grasp on the B-Fighters' powers, Gaohm allows them to kill him in episode 18, then uses the energy from it to revive himself in a One-Winged Angel form.
- Transformation Trinket: Handheld devices called the B-Commanders.