Artificial Humans: The entire Mibu tribe in the manga, who are revealed to actually be the Battle Dolls of the True Mibu. Except Kyo, the last of The True Mibu. Flipped in the anime, where only Kyo is a Battle Doll.
Ax-Crazy: Ninety percent of the main cast is this, including the title character
In the anime, it's strongly implied Saizō has a crush on Yukimura. It's not helped by Yukimura teasing him ( "What are you, my wife?" followed by "If it pleases you, my lord". Then there's Saizō blushing and his comment when Yukimura disguises himself as a woman. The kimono "really suits you" indeed.)
While not exactly a bodyguard, Hishigi seems to be this for Fubuki. He throws himself in front of Kyo's most powerful attacks for him, and his only concern seems to be for Fubuki's survival.
Elemental Powers: Subverted. Hotaru, the fire user, is calm, while the ice user, Akira, appears calm on the surface, but push a few buttons and he loses his head. Not to mention that Shinrei, the water guy, loses his cool even more easily.
Elemental Rock-Paper-Scissors: Averted; It's demonstrated over the course of the series that the superiority depends on the wielder, rather than the element they are using. Hotaru initially wins out against Shinrei despite severe injuries from fighting Kyo, but only because he's using His Hono Chikewai, which gives him a huge boost of power, but causes damage over time. Shinrei ultimately comes out on top because Hotaru's boost wears off. And of course, both of them get mercilessly curbstomped by Fubuki.
Four Is Death: The Shiseiten are frequently described as being gods of death. Most of the Taishiro are even more lethal.
Gentle Giant: Bontenmaru. Sure, he has the whole "god of war" thing going on, complete with a berserker mode and everything, but he has a soft spot—not like that—for little girls, even ones that punch holes in him and torture him; and Akari reveals that he likes shoujo manga. As for Bontenmaru's reason for taking over the entirety of Japan? He wants to take it over so people can live their lives in peace.
A God Am I: The vast majority of the Mibu think like this. And in truth, no one really disputes them on that.
The manga lampshades this by having Akari take Yuya's gun and attempt to shoot Santera with it. Santera stops the bullets, and Akari throws the gun away.
He Who Must Not Be Seen: Sakuya spends 32 volumes hidden behind her bangs, and the manga-ka is fond of "lighting" characters whose faces we aren't to see yet from the back, or putting them in elaborate, face-covering costumes
Homage Shot: The manga opens with a lay-out and narration content ridiculously reminiscent of the first page of Rurouni Kenshin, which was still running at the time. The series probably originated as an attempt to cash in on Ruro Ken's popularity as historical drama with legendary swordsman incognito, but found its own very weird voice pretty quickly.
More precisely: SDK's first page runs, page-width panels going down:
[First panel: bloody battle scene; whole page has artful blood drips all over it] "During the end of the warring states period... In a time of chaos, a war began to try to divide the country. This fight would later be known as the Battle of Sekigahara. Like thunder the war spread. Under this sound and bloody rain, many were killed."
[Second panel: 'shadowboxing' image of dramatic duel] "These warriors, without taking care for the issues of the battle, had found the meaning of their lives in sword-handling... They lived only to improve their skill... And died..."
[Empty white bridge space extending across page] "Among the men who disappeared at this historical time..."
[Third/final panel: bottom of page occupied by close up of Scary Eyes (Red Eyes, Take Warning in this case, but the manga's in black and white, so you can't tell)] "There was one who was called 'the unbeatable'..."
[Two-page title spread, then complete tone-shift and Kyoshiro as The Ditz reading off a wanted poster, finishing the sentence] "The legendary wanted man, Demon Eyes Kyo."
Meanwhile, Ruro Ken starts with, also page-width panels:
[First panel: blood spatter flying] "One hundred and forty years ago, during the bloodbath in Kyoto touched off by the coming of Commodore Perry's black ships...there was a man known as the 'Hitokiri Battousai.'"
[Second panel: similarly composed bloody combat scene, with our hero central] This man was a major player in the Meiji Restoration, for his skill with a sword was unrivaled. Once the war was over, he vanished without a trace. Time passed and legends formed, of how he was the strongest samurai to walk the face of the earth."
[Third/last panel: Scary Eyes Important Scar closeup] "And so, our story begins... In Tokyo, on the eleventh year of Meiji..."
[Two-page title spread, next page opens with Kaoru's shout] "HITOKIRI BATTOUSAI!"
Jekyll & Hyde: Kyo and Kyoshiro. Subverted in the manga, played straight in the anime In the Alternate Universe of the anime, Devil Eyes Kyo is actually the Id of Kyoshiro which he split from himself and placed in an Artificial Human body; they later reunite in their original body after Kyoshiro defeats Kyo, but this time as split personalities.
Medium Awareness: Kyoshiro vs Benitora: "Can we just pretend the last 5 pages didn't happen?"
Mobile Menace: The Mibu never seem to be inconvenienced by the size and complexity of their lair, except for when they've pulled a Heel-Face Turn, in which case, they have to slog it out with the other heroes.
Obfuscating Stupidity: Hotaru is a good example, but the real winner is the Former Crimson King, who acts like a nearsighted buffoon who's Blind Without 'Em. Tokito, who got taken in by the facade, actually starts plotting to overthrow him until the Former scared the living daylights out of her with murderous intent, showing Tokito and readers the true nature of the Former Crimson King.
In the manga at least. In the anime, there's only Yuya's crush on Kyo/Kyoshiro and their growing feelings for her. They are shown to have gotten together in the epilogue in the last episode — where Kyo and Kyoshiro have been reunited into a single individual — which takes place years later. Also Benitora and Mahiro in the ending of the anime as well.
One Head Taller: If Kyo wore a Western-style button-down shirt, Yuya would hold conversations with/have infuriated outbursts at his breast pocket.
One-Man Army: It would be easier to list the characters who AREN'T one.
Running Gag: Hotaru trying to move caterpillars out of the way so they don't get crushed during fights
Samus Is a Girl: Tokito, who stops Bontenmaru's fists with three fingers and actually punches through him, despite the fact that one of his biceps is bigger around than her waist, not to mention that she completely pwns the crap out of Akira for most of their fight.
Admittedly, some fans weren't convinced she was a boy in the first place.
Tsundere: Kyo is heavy on the tsuntsun, regularly calling his Love Interestdog-face and Servant #1, and has a really obnoxious habit of randomly feeling her up, no matter who happens to be watching. But the few moments in which he shows that he cares about her and the way he fights when she's in danger are surprisingly genuine and heartwarming, especially near the end of the manga.