Action Survivor: Akamatsu Industries, mostly. Were as everyone else is dropping like flies, Akamatsu employees (especially Li-chan and Yamajii) manage to stay alive.
Air-Vent Passageway: The heroes end up traveling in some very tight vents at one point. However, it not because they're trying to hide, but the only thing that's keeping them safe is effective in enclosed spaces.
All There in the Manual: The "Mode Warp Files" on the DVD extras, plus the supplementary leaflets accompanying the DVD volumes. A defunct website once provided background info on the characters.
All Your Base Are Belong to Us: Akamatsu Industries gets attack twice by their enemies. Fortunately its after hours, and most of the employees have gone home.
Almost Kiss: A total of three times between Keita and Hinoki. They never actually kiss for real, either. The closest they ever get turns out to be All Just a Dream.
Amusement Park of Doom: Bottom World, after its employees go insane and reprogram the attractions to be hostile.
Artistic Title: The opening consists of Live-action footage of a coral reef, with images of the characters superimposed.
Awesomeness by Analysis: Both the Betterman and the Neuronoid analyze their enemies to customize their attacks to match.
Battle Couple: This occurs when the Dual Kinds couples are piloting their Neuronoids. (Kaede and Shou, Hinoki and Keita.)
Kaede and Shou become this literally after tying the knot near the end of the series.
Bittersweet Ending: A good chunk of the main cast is dead, as is Yakusugi and most of the Bettermen. However, they managed to succeed in saving humanity, and Kaede‘s and Shou's preborn child is saved by Chandi.
Bug War: Professor Umezaki has a legion of insects and other horrors at his control, which he uses to carry out his schemes. Our heroes end up fighting them.
The Cavalry: Betterman Lamia for the most part. Yakusugi and Lume for Lamia. Chandi for Keita.
Chekhov's Gun: Several in the series - dams, wooden bells, insect repellent devices, etc.
Clothing Damage: Keita and Hinoki's dive suits from the beginning episode and final episode. Also happens to Asami in the final episode.
Cool Old Guy: Yakusugi, who saves the entire cast on several occasions. Akamatsu could count too, even though he's not quite as old as Yakusugi.
To be fair, nobody's as old as Yakusugi.
Cryptic Background Reference: In episode 2 while watching footage of Betterman, Asami makes a reference to "The cry heard when the Aryan people ate the Soma!" Other than referencing "Soma" occasionally, Asami never elaborates on this.
Dead Hat Shot: After Kaede succumbs to Algernon and causes the mecha she and Yanagi are in to explode, her cracked hair barrette is seen floating away in the water.
Death World: The setting is becoming this - Algernon is causing mass insanity (though not quite pandemic). Biological horrors and runaway machinery create havoc, and even hospitals and amusement parks are not safe. The heroes barely survive, and need Betterman to have a fighting chance. Things get so bad that even Betterman falls prey, and another Betterman or Yakusugi has to save the day. And even those backup heroes end up kicking the bucket!
Distressed Damsel: Happens to Hinoki, Asami, Kaede and Sakura over the course of the series. For some reason, the three well endowed girls get multiple instances of this trope while the loli of the group gets only one.
Dream Weaver: One of Mamon's agents. Using a charm given to Keita, a psychic causes our heroes (even Lamia and Bodaiju) to fall into a long and confusing dream state.
Drowning My Sorrows: After surviving yet another horrific monster attack, Yamaji and Li-chan drink a lot of beer.
Eldritch Abomination: True to being a bio-horror series, there's a ton of nightmare inducing monsters. Kankel takes the cake, being an entity that seeks to assimilate all Earthly life.
Empty Promise: When Hinoki is worried about Keita joining the team, Sakura assures that he'll be alright. She lied. She has no idea if he'll survive, but was touched by Keita's kindness. Plus, she wanted to be close by a normal teenager.
Enemy Within: Kankel. Yakusugi is connected to the monster, as he was the subject of the Dive Inspection. Though he attempts to stop it, Yakusugi ends up being taken over.
Evilutionary Biologist: The main reason why the antagonists are doing the things they do is to ensure the survival of humanity. Subverted - it turns out they were afflicted by Algernon, and the resulting insanity causes them to go such extreme, crazy lengths.
High-Tech Hexagons: Our heroes encounter a number of strange hexagonal walls while dealing with Umezaki. They’re really aligned giant bugs created using biotechnology.
Hope Spot: Heichin may be insane, but they may be able to save his life... until he gets kidnapped and stuck in a holding tube. But wait, he's still alive! Until he disappears, and his ultimate fate is revealed.
I'm a Humanitarian: Sort of. Those Animus seeds that Lamia eats to transform, the ones that feed his species, are from flowers that grow from dead humans. In other words, Somniums eat people. The squick is not lost on Akamatsu and one antagonist later calls Betterman out on it. This is also part of Dr. Umezaki's plan to solve world hunger by using the Animus flower, which grows only from dead people.
Irony: Both Tragic and Dramatic. Asami, who has spent years trying to find a way to stop the Algernon virus from spreading, finds out that she is in fact a carrier of the virus. She's then killed by Chandi, who is hunting down the carriers of Algernon. Chandi had also killed her creator, Dr. Umezaki, (who was yet another carrier) several episodes earlier.
Kaiju: Betterman's combat forms and several of the horrors he faces.
Killed Off for Real: Lots of people, fitting for an anime series of this genre. Out of the main characters, only Keita, Hinoki, Shigeru and Sakura survive.
Laughing Mad: If you're possessed by Algernon, you're probably going to be doing this a lot.
This happens to almost the entire main cast at one point, due to Dr. Umezaki's pheromone attack.
Madness Mantra: Heichin endlessly repeating the number 26 after being afflicted with Algernon.
Mega Corp.: Mode Warp, which has enough resources for building high tech robots, easily acquire advanced military equipment, and has Special Forces on hand for emergencies. Not that it matters, as anyone from Mode Warp that's not Asami is fated to be a Red Shirt.
The Merch: This series has spun off two drama CDs, one set of anime trading cards, various resin kits that involve the girls, statues based of the different forms of Betterman, a manga, and a garage kit of one of the neuronoids. Not to mention two hobby magazines that give information about the show itself.
Midair Repair: In episode 3, our heroes are stuck on a falling airplane. Fortunately, Betterman can use his powers to pilot the aircraft and keep it flying.
A Mind Is a Terrible Thing to Read: A psychic condition called the limpid channel allows you to read the thoughts of anyone around the world. Sakura can't control hers, and is mentally bombarded by the thoughts of everyone around her 24/7 unless confined to a special chair called the Manage Machine.
Moment Killer: Keita is a constant victim to this trope when he is alone with Hinoki.
Monumental Battle: The Ajanta Caves. While not as well known as other world landmarks, the caves are a real world Buddhist cave complex.
Mystery Arc: The first half of series had these arcs. It begins with an investigation of mysterious events. Once its clear something strange is going on, Keita and the team end up investigating (or finding themselves in the middle of) the issue, were they come across data and plenty of bad guys. After some fighting, the group then discuss their findings.
N.G.O. Superpower: The Next Environment Organization. (NEO) is the parent organization of Mode Warp BPL, and the Superhuman Federation.
Nonstandard Character Design: Keita and Hinoki have very different designs from each other. However, the show manages to integrates the designs well enough that it isn't distracting.
On the Next: The previews at the end of the credits has Sakura provide a haunting narration. During the Tech TV broadcast, the Announcer would state "On The Next Betterman" before the preview was shown.
Powered by a Forsaken Child: In one episode, while fighting off an "unmanned mecha", Shou discovers it's controlled by the brain of his "deceased" brother. The "Mode Warp Files" are even more disturbing. The Neuronoids first built by Mode Warp requires eight human brains each to operate.
Applied Phlebotinum: The Linker Gel, which allows operators to pilot the Neuronoids with their thoughts.
Awesome but Impractical: Useful in fighting monsters, getting data, and protecting people from harm. But they’re extremely convoluted (requiring two Dual-kind operators, flipping over to change modes, needing to recharge its gel, etc.) for conventional use.
Black Box: According to the "Mode Warp Files", there are mysterious "Black Boxes" that act as computers for the mechs. The company is reluctant to discuss what's in the boxes. It turns out that they contain brains.
Calling Your Attacks: SYNAPSE ATTACK! Justified, as several of the Neuronoid's actions are voice activated.
Dual Mode Unit: Has an "Accept" and "Active" Modes. Accept is used for gathering data and analysis, and uses less linker gel. Active increases the mecha's speed, agility, and allows for the Synapse attack. The down side is that it uses more gel.
Improvised Weapon: Being used for investigation of hazardous areas, Neuronoids carry no conventional weapons. But being giant mecha, they can basically pound anything with their limbs. In addition, there's the Synapse Attack - using collected molecules in the air, the mecha can create any chemical to strike back with.
Rollerblade Good: In it's action mode, the mecha can move fast using wheels on their legs. Useful in battles, and to avoid falling debris.
Red Shirt: The main characters are often the only survivors of whatever horrific events they witness. It's rare to see anyone who's not part of Akamatsu Industries or a Betterman last more than a few moments on screen.
Red Shirt Army: Mode Warp's support personnel. And when the military tries to help they don't last long either.
Rescue Arc: Sometimes overlaps with the Mystery Arcs.
Running Gag: Keita being late for school, and then running into something.
Scary Shiny Glasses: Asami and Keita have plenty of these moments. In fact, any character who wears glasses is bound to display this trope at least once.
Science Hero: The mundane main characters, who use technology and science to investigate Algernon and stop the antagonists.
Shout-Out: The Akamatsu Industries Company shares the initials of animation company AIC.
Single-Target Sexuality: Shou only ever has eyes for Kaede, and he's quite distraught when she's kidnapped by Mamon.
Spell My Name with an "S": Several characters, but Li-chan is the most prominent. Her name is Ritsuko, but her nickname sounds like "Li-chan" instead of "Ri-chan".
Techno Babble: The series is infamous for the overuse of this. Oddly enough, the technobabble makes some sense, if you've taken College Biology. Not that it matters, most of the fictional elements seem to work based on plot than actual science.
There Is No Kill Like Overkill: It seems like a bit much to use two giant robots to investigate a medical epidemic, and ones that require a rather convoluted scheme to function, at that. But as the series continues, it's clear that even the mecha are not enough.
Those Two Guys: Yamaji and Li-chan become this after Heichin contracts Algernon and is committed.
Unwanted Rescue: A minor example. When Keita first meets Sakura, she's appears to be restrained to a machine. When he tries to take it off, Sakura quickly explains that she is actually fine. The chair turns out to be a medical device, and Sakura could leave it without aid.
Vagueness Is Coming: Algernon, which doesn't get a decent explanation until many episodes latter.
Voodoo Shark: One episode featured a Principal who went on a rampage turned out to be under mind control. The welding mask he wore contained a device that resulted in his behavior. Of course, that does bring up the question of what would the school Principal be doing with a welding mask in the first place. Or how he would not notice the large spike on the interior of the mask. Or not question why a welding mask would be filled with electronics...
Wartime Wedding: Shou and Kaede have a somewhat hastily-thrown-together one near the end of the series, after announcing that she's pregnant.
We Have Reserves: With Cactus dead, Asami suggests using Keita as a replacement. An annoyed Akamatsu lampshades the implications, to her immediate remorse - she hadn't meant to sound callous.