Badass Decay: Eiji starts off the series a no-nonsense hunter able to fight Ashu even without being a Boukenger, but after he joins the team he becomes a less serious and much more comedic.
Base-Breaking Character: Natsuki. You may like her for having an interesting character arc and her cute appearance provided by Chise Nakamura or hate her for doing many dumb things that may even endanger her own team.
Bizarro Episode: The aforementioned Task 39, coupled with Clip Shows of past episodes (first as they try to figure out which villain sent them the Prometheus Stone, then when its bomb is accidentally activated and everyone decides to stay together when it goes off). As it turns out, it was Makino-sensei who gave them the Stone as a form of training, and they stopped the bomb in the nick of time by smothering the Stone in Aegean salt. That is, no henshin, no mecha fights, and Eiji and Masumi dancing hula among other things.
Broken Base: The suits. Are they the most awesome thing ever, or way too cluttered and ugly?
Creator King Ryuuwon is the ruler of the Jaryuu Clan and a former human alchemist who desires to supplant humankind with his own genetically-engineered Master Race. Believing strength is everything, Ryuuwon frequently sacrifices his men in ritualistic duels to the death to create Wicked Dragons, once even making 3000 of them kill each other for a ritual, and also blows several of them up in an attempt to kill the Boukengers. For one scheme, Ryuuwon partnered with the Questers to brainwash Natsuki Mamiya into using the Sun of Lemuria to wipe out humankind. When his mutation wears off and Satoru offers him a chance at redemption, Ryuuwon rejects it, not content to live if he can't be superior to others.
Yaiba of Darkness is the deputy leader and most dangerous member of Dark Shadow. Having slaughtered Masumi Inou's adventure party in the past, Yaiba only spared Masumi in the hopes of corrupting him. Championing the power of darkness above all else, Yaiba eventually betrays Gekkou of Illusions and unseals the Demon Bird from within him to kill the Boukengers, delighting at getting to witness its world-destroying power. He later coerces Masumi into helping him summon a meteor to crash into Earth and plunge the planet into darkness, creating an environment where only darkness beings like himself can thrive.
Designated Hero: Satoru earns this title in Task 11. He lied and alienated his teammates, betrayed Souta's trust, hurt Natsuki's feelings, overall kept everyone in the dark, jeopardized the mission and purposefully got their mecha captured, thus potentially risking the lives of millions of innocents (he didn't, but it was out of pure luck), all of that just to satisfy his adventure boner.
Evil Is Cool: Boukengers definitely has some of the coolest villains in the franchise.
Yaiba of Darkness, a badass shadow-themed ninja who's a competent and formidable threat to the Boukengers whenever he appears.
Natsuki/Bouken Yellow being a Lemurian Princess would seem strange, unless you realize that back then in Dai Sentai Goggle Five, Lemuria is the civilization symbolized by Goggle Yellow.
In Task 22, several members of the team (Masumi, Natsuki, and Satoru) are transformed into different animals. Masumi is... A German Shepherd. However, this actually makes a lot of sense; Shepherds are favoured as police and army dogs, and are generally considered dangerous and aggressive. In reality, however, they are actually quite intelligent, friendly, and loyal—quite bit like Masumi himself. He comes across as the mean 'bad boy' of the group, but actually cares quite a lot about the team, and is much nicer than he originally gives himself out to be.
Unless their numbers are being multiplied by special effects, you only seem to see a maximum of three Jaryuu on the screen at once, much like Land of the Lost (1974) where you only saw three Sleestacks on camera at once because that's how many costumes they could afford.
This ended up happening again in the next anniversary series with the Sugormin, except in this case, it was because Toei only made 3 costumes as opposed to just not being able to afford more.
On the topic of Gokaiger, AkaRed’s gimmick of transforming into past Reds ends up being a precursor to the Gokai Change, where the Gokaigers can become past Rangers. It makes sense when you remember AkaRed was Marvelous' mentor, and he may have found a way to infuse this ability into the Mobilates, seeing as how the Gokaigers are capable to perform Gokai Change into other Sentai warriors even after returning the Greater Powers to their rightful owners.
Episode 35 gives us a version of Momotarou. The Kamen Riderseason that would air after Boukenger gave us a new twist on the concept.
SGS aren't the only ones who measure things in Hazard Levels. Not to mention the fact that a "Pandora's Box" relic plays a role in the plot late into the show.
At the beginning of #26, Natsuki imagines herself as Cinderella in the fairy tale, with Sakura as the prince.
In #23, Gai reads Souta's mind to get information on a Macguffin and Souta trolls him by thinking of cute girls he's met instead. When Gai threatens him, Souta imagines Satoru and Masumi shirtless instead and asks him if he's happy.
Love to Hate: The Questers and Gai in particular, whose hamminess and trollish charm make him a very fun villain to hate on.
Gai, Rei, and Ryuuwon's comes in Task 33 when they brainwash Natsuki after she's revealed to be a Lemurian Princess into believing her parents wanted her to wipe out humanity.
Yaiba of Darkness' comes in Task 44 when he backstabs Gekkou and Shizuka and unseals the destructive Demon Bird to kill the Boukengers before leaving them all for dead.
Narm: The way Gajah talks, from his intonations to his facial expressions, makes it damn near impossible to take him seriously.
That annoying kid from Task 5, who fails to recognize that Sakura is BoukenPink despite all the obvious clues.
The adventurer from Task 29, who spends most of the episode being whiny and irritating and berating Satoru and the other SGS members.
Tear Jerker: Episode 25 sees Eiji befriend Akutagami, an ineffectual Tsukumogami who becomes intelligent through eating the episode's Macguffin. At the end of the episode, Akutagami comes up with a plan to fake his death to free himself from Dark Shadow's services. Eiji is happy to seem him alive, only to find that the Macguffin's effects wore off and Akutagami doesn't recognize him. The episode ends with Eiji telling Akutagami to hide in a forest and live freely away from Dark Shadow.
They Wasted a Perfectly Good Character: Ouga, an Ashu King who leads a separate tribe from Gai's and is implied to be more dangerous than him, who also shares history with Eiji's mother. Despite this, he only serves as the Monster of the Week for a single episode and gets no further development.
The first episode establishes a rivalry between Satoru and Masumi. This all but disappears by the next episode and for the rest of the series, they get along perfectly fine, until the endgame arc where Masumi reads his diary and starts being a jerk towards Satoru for no reason.
A couple episodes imply that the SGS doesn't fully trust the Boukengers and may be hiding things from them. This leads to... absolutely nothing.
The Movie for the series begins with all four Negative Syndicates gunning for an extremely powerful Precious. The Negative Syndicates battling each other and the Boukengers having to elude them while working to obtain a Precious could have easily sustained the plot of an entire film, but instead they mostly serve as Starter Villains and an unrelated villain serves as the Big Bad.
, courtesy of Saint Seiya artist NoB.