Mai-Otome Zwei

A four-episode OVA sequel to Mai-Otome, taking place exactly one year after the original.

Until the fourth and final episode was released, most forum threads dedicated to this series had been filled Epileptic Trees of various degrees of plausibility. But it seems that the actual episode only muddled the waters in the shaky continuity-discontinuity relationship between My-HiME and Mai-Otome even more. It did, however, get a number of fan-theories about the Otomeverse Jossed.

It remains to be seen whether the follow-up, a prequel series named Mai-Otome 0~S.ifr~, will be of any help. And now they're throwing characters from the Mai-HiME Destiny spin-off novels into the equation...

Has an attendant manga that follows from the original anime but eventually diverges from the OVA and is not linked to the original manga.

Tropes used in Mai-Otome Zwei include:

All Just a Dream: Subverted. Arika assumes that she was dreaming about destroying the meteor, but Maria points out that it did actually happen.
The Atoner: Nina.
Back-to-Back Badasses - Arika and Mai in episode 1. Arika and Nina in episode 4.
Big-Budget Beef-Up
Big Freaking Gun:which is as useless as ever
Bruce Wayne Held Hostage - Subverted: Arika is sleepy, doesn't realize what's going on, and thus screws up what could be a more peaceful resolution; on top of that she couldn't use her Otome powers anyway. It doesn't help that Tomoe identified her to the busjackers purely out of spite.
Can't Hold Her Liquor - Ahn Lu, Annam's Otome in episode 3, gets drunk in a relatively short period of time, forces Arika's face into her breasts and strips off the fellow Otomes' tops
Chewing the Scenery - Several scenes have this feel to them.
Combination Attack - Arika does a Bolt From the Blue through one of Mai's rings of fire to kill the first Child, and Arika and Nina combine their ultimate attacks to finish off the Big Bad.
Continuity Nod - Nao, reads an entry from Sergay's diary about the magazine with pictures of Nina and a few other students that Nao took in one of the specials.
Conspicuous CG
Death From Above
Dork Horse Candidate - Wattarl Ishigermin and his running mate Tomoe. The citizens consider the former an annoyance and show outright hatred and disgust toward the latter.
Ecchi - The bath scene goes beyond "Fan Service."
Empathic Weapon - Arika's Zwei Robe.
Failsafe Failure - the Surrogate System.
Fan Service
Fan Service Pack - During the year after Mai-Otome, Arika's robe wasn't the only thing that received an upgrade.
Faux Action Girl - As in the original series, Natsuki's attempts to actually fight are routinely fruitless and cut short.
Giant Space Flea From Nowhere
Good Costume Switch - Nina's new Meister Robe.
Great Big Book of Everything - Subverted: it's not actually a book at all
Guilty Pleasures - No plot? No problem!
Hit Me Dammit - Arika and Mashiro. Doubles as Get a Hold of Yourself, Man!.
Hot Springs Episode - Most of episode 3 is the Otomes spending their time while everyone else is at the SO.L.T. conference, which for obvious reasons, they weren't invited to.
- Except for Kazuya, who is for some reason at the hot springs with the Otome instead of at the conference, despite being one of the three emperors of Cardair.
Lampshade Hanging - Nao and Nina comment out every single Temple of Doom trope they encounter.
Nipple-and-Dimed - A half-second of pink nipples in the third episode, right in front of the camera.
The Nose Bleed - Kazuya, after the Otomes' swimsuit tops are pulled off, causing Akane to slap him.
Phlebotinum Breakdown - The Surrogate System, constantly and by design.
She's Back - Nina, after a Ten-Minute Retirement in the end of the main series
Shout-Out - To My-HiME, even more of them than in the original series.
Sorting Algorithm of Evil - Yuna is arguably an even greater threat than Nagi, with the potential to destroy the entire world.
Talking Is a Free Action - Yukino is able to give the entire speech for activating Haruka's GEM while falling with her, and Haruka Materializes just as she hits the ground.
Tempting Fate - After Nina describes the first trap as a pit trap upon entry, Nao wonders who would fall into it, just as Nina triggers it.
The Worf Barrage: - Arika Bolt from the Blue, even in Materialize Zwei, generally fails to kill the monsters unless someone else launches an attack with her.
What Kind of Lame Power Is Heart, Anyway? - Some of the Otome's powers.