Japanese Beetle Brothers

Japan loves bugs, and they're everywhere. Not only is Bug Catching one of the oldest pastimes in the country, but much of their pop culture includes or is influenced by them.

However, within Japanese media, two particular insects stand out: the Kabutomushi (Japanese Rhinoceros Beetle, though often romanized by the Japanese as simply Beetle) and Kuwagatamushi (Stag Beetle). Often, when something inspired by one of the two appears in some sort of media, the other is either with them, or not too far behind. Another common element is for the two beetle-inspired elements to be of contrasting colors, and there is often a Red Oni, Blue Oni relationship between the two.

There have been enough examples that they can be organized into three types:
 * Type A: Allies. They are usually introduced at the same time, constantly work together and are seldom seen apart. Often Type As are either partners or brothers.
 * Type B: Rivals. They can't stand each others' guts, constantly butt heads and at times are on opposite sides.
 * Type C: Coincidental. This is the rarest of the three types, and occurs when just by chance, and Kabuto and Kuwagata exist in the same universe, much like their real-life counterparts.

Related is the Beetle Sister, the Tentomushi (Ladybug, a.k.a. Lady Beetle). Whenever beetles form a Power Trio, you can expect The Chick to be a Ladybug.

Rarely, this phenomenon will be referenced obliquely. If two characters with some sort of relationship exist in your medium - and one has a single horn (shut up) and the other has two, chances are this is why.

Anime and Manga

 * Medabots has a prime example of a Type B in Metabee (the Kabuto) and Rokusho (the Kuwaga), who are Gold and Silver, respectively, and have extremely different personalities, as well as the nature of their Medals, though sometimes cross into being Type A as Rokusho will sometimes offer his assistance to Ikki and Metabee.
 * Digimon has a Type B in the form of the blue Kabuterimon and red Kuwgamon, though this is mainly in accordance with supplemental material. The anime makes it seem more like they are a Type C.
 * Plus there's Kabuterimon's pre-evolution, Tentomon, closing the aforementioned Power Trio.
 * An oblique reference exists in Milleniumon, a Biological Mashup of two Hybrid Monsters already famous for being a combination of parts of other Digimon: the biological Kimeramon and the mechanical Machinedramon. As Milleniumon progress through its multiple forms, the one thing that will remain constant is that one head will have a single horn and the other will have two.
 * By extension of the Pokémon video games, we have the Type C pair of Heracross and Pinsir.
 * In the episode where Ash catches his Heracross, a bunch of Pinsir are invading the Heracross herd's territory, making it seem like a type B, but it's revealed that the invasion is due to the Pinsir being driven out of their own territory by Team Rocket.
 * Type A in One Piece during the Thriller Bark arc. Usopp uses two different large slingshots named Kabuto and Kuwagata.
 * Zoids features the beetle-type Zoids Saicurtis (a red Kabutomushi) and the Double Sworder (a blue Kuwagatamushi) in a type B scenario, with the Saicurtis as an Imperial Zoid and the Double Sworder as a Republican Zoid. Both apppear in Zoids: Chaotic Century- however, the Saicurtis only appears in the manga, while the Double Sworder only appears in the anime, though the Saicurtis was mentioned by name in the anime.

Live Action TV

 * The Metal Heroes series Juukou B-Fighter and its sequel B-Fighter Kabuto each have the three-man version of Type A with a ladybug; the former with Blue Beet, G-Stag, and Reddle and the latter with B-Fighter Kabuto, B-Fighter Kuwaga, and B-Fighter Tento. This extends to their American counterparts, Big Bad Beetleborgs/Beetleborgs Metallix (Blue Stinger, Green Hunter, and Red Striker Beetleborgs; and Chromium Gold, Titanium Silver, and Platinum Purple Beetleborgs respectively).
 * B-Robo Kabutack also had a three-man Type A with Kabutack, Kuwajiro, and Tentorina.
 * Kamen Rider has also inevitably used this, having a preference for insect themes:
 * Averted in Kamen Rider Stronger. The series featured a Rhino Beetle-themed titular hero and female Ladybug-themed sidekick, but no Stag Beetle.
 * One of the most powerful enemies faced by stag beetle-based Kamen Rider Kuuga is a rhinoceros beetle-based Grongi, Go Gadoru Ba. Leader of the most powerful of the Grongi tribes (though not the leader of the Grongi as a whole himself), Gadoru was one of three Evil Counterparts (the other two based on a grasshopper and a stag beetle) to Kuuga, and who was able to change between different forms corresponding to Kuuga's forms. Interestingly, even as Gadoru was the second most powerful Grongi in the series, the leader of the Grongi was the aforementioned stag beetle-based Grongi leader, N Daguba Zeba.
 * Kamen Rider Blade is another prominant Type A example, with the rhinoceros beetle-based Kamen Rider Blade, and the stag beetle-based Kamen Rider Garren. Moving away from the pattern a bit is the mantis-based Kamen Rider Chalice, and later the spider-based Kamen Rider Leangle.
 * Kamen Rider Faiz has another villainous Type A example in the beetle Orphenochs introduced in episode 33.
 * Kamen Rider Kabuto has the red rider Kabuto, and the blue rider Gatack, who start out as Type B, but eventually become Type A, who are probably the best-known example of this trope.
 * Kamen Rider Double has a semi-Type B with the black and red Stag Phone and all-blue Beetle Phone, belonging to Double and Accel, respectively.
 * Anyone else notice how the W on Double's helmet and the A on Accel's are patterned after the same beetles?
 * Kamen Rider OOO has a villainous Type A in the Kabuto and Kuwagata Yummies, which formed when a single Yummy (which was the Kabuto one) split in two. But averted in that OOO has a Kuwagata Core Medal, but not a Kabuto Core Medal.
 * Of course, Super Sentai and Power Rangers aren't left out either:
 * Ninpuu Sentai Hurricanger has the one of the strongest examples of Type A in recent history, with the Denkosekka Gouraiger. The Gouraigers are comprised of the crimson red Kabuto Raiger and navy blue Kuwaga Raiger, brothers whose entire motifs, changers, personal weapons and mecha revolve around the Kabuto/Kuwaga pair.
 * Once again, this can be extended to the Thunder Rangers from Power Rangers Ninja Storm, who are also brothers (though by adoption, not blood).
 * Juken Sentai Gekiranger has a lesser Type A example in the Yin-Yang influenced white Butoka and black Wagataku, who are similar to terracotta soldiers, have no personality, yet get an upgraded form after their initial defeat. These two appear in Power Rangers Jungle Fury as the Shadow Guards.
 * In Tensou Sentai Goseiger is something somewhere between Type A and Type C with the existence of the Kabuto and Kuwagata headers.
 * Tokumei Sentai Gobusters, like Hurricaneger, has a pair of Sixth Rangers - Beet Buster and Stag Buster. It should be obvious which animals their motif is.
 * Chouseishin Gransazer has a Type A in the form of the Wind Tribe's Sazer-Remls and Sazer-Dail.

Toys

 * The Machine Robo Mugenbine toy line has the Type A red Iron Beetle and blue Junk Stag that can combine together to become Mugen Sector.
 * The Transformers Insecticons Barrage and Chopshop, who fit the bill as a basic Type A, were toy-exclusive.
 * Those toys (along with the other Deluxe Insecticons) came from a defunct Bandai line called Beetras; had the line continued, there would have been a female lady bug character/toy as well, which could have been the first official female Transformer.

Video Games

 * Pokémon originally just had the Stag-based Pinsir, and didn't get its Type C until Heracross was created in Generation 2, which also added Ledyba/Ledian. Oddly, Kabuto and Kabutops are not examples, being based more on horseshoe crabs. Their name comes from traditional kabuto, which are samurai helmets. That's why the Dome Fossil is called so.
 * The Digimon video games have this, and due to the increased detail can expand further on this than the anime. The Kabuto- line includes champion level Kabuterimon, ultimate level MegaKabuterimon (in blue or red) and mega level HerculesKabuterimon or TyrantKabuterimon. The Kuwaga- line includes champions Kuwagamon and BladeKuwagamon, ultimates Okuwamon and MetallifeKuwagamon, and megas GranKuwagamon and GrandisKuwagamon. At those points, the lines are Type B. However, at the Rookie level, Tentomon, Kokabuterimon and Kokuwagamon aren't as opposed. One additional mega for the general beetle themed Warriors of Thunder line is AncientBeetlemon, which decidedly has traits of both.
 * While the original Medabots games, which were usually separated into Kabuto/Metabee and Kuwagata/Rokusho versions, had those two Medabots, they had more of a Type C relationship.
 * The card battle game Mushiking has both the Kabuto and Kuwagata, but since they're not characters in a story, they're relegated to Type C.
 * Among the bugs you can catch in The Legend of Zelda: Twilight Princess, there are the Kabuto(referred to simply as a Beetle) and the Stag Beetle, putting it into Type C.
 * Yamato (Kabuto) and Shoya (Kuwaga) from Drone Tactics are Type A.
 * Monster Rancher has the Beaklon (Kabuto) and Antlan (Kuwaga). They're sort of a mid-range between Type B and Type C—they weren't introduced at the same time and just sort of coexist, but their battle styles are different enough to seem contrasting.
 * Mega Man X has a Type A setup with the first game's Boomer Kuwanger (a not-very-good translation of Kuwaga) and his brother, the third game's Gravity Beetle, who is of the Kabuto variety. The latter is actually one of the few Mavericks in X3 who is completely uninterested in Doppler's plans and isn't even infected with The Virus, but instead seeks revenge. In the manga, he even attempts to rebuild his brother.
 * Mega Man Zero has a similar Type A with the first game's Herculious Anchortus (Kabuto) and the second game's Kuwagust Anchus, who refers to Herculious as his brother and teams up with him during the Boss Rush.
 * Less dramatically, the first Megaman Legends game contains a sidequest where the player can collect junk and trade it for valuable components. Two of the trade items are a Beetle and Stag Beetle pair, each of which can be found crawling around the forest.
 * Mega Man Star Force exhibits this trope in Black Ace/Red Joker. The Red Joker Finalization has the two horns of the kuwagatamushi and the Black Ace sports the Kabutomushi's single horn.

Western Animation

 * The original Transformers cartoon had the insecticons Bombshell and Shrapnel, who are Type A by nature. However, their Power Trio is rounded out by Kickback, a grasshopper.

Real Life

 * The rhinoceros beetle and stag beetle are normally Type C, but in the hobby of Insect Fighting, they become more of a Type B