My-Otome Zwei takes place one year after the events of My-Otome. Arika is now a full-fledged Otome (though still under the tutelage of Miss Maria) and Nagi is incarcerated in a prison somewhere in Aries. The various nations are at peace with one another and plan to hold S.O.L.T. (Strategic Otome Limitation Talks) to discuss limiting the numbers of Otome.
A mission to destroy a meteor threatening to collide with Earl sets into motion a chain of events which result in a mysterious shadowy figure attacking Garderobe and several Otome as well as a new, more powerful version of Slave appearing across the planet. To make matters worse, Queen Mashiro disappears following an argument with Arika. The series follows Arika's search for Mashiro as well as Garderobe's attempts to uncover the truth behind the shadowy figure.
One year after the political intrigue and descent into war of Mai-Otome, the world is trying to heal its wounds. Otome from different countries work together to deflect an asteroid in danger of hitting the planet, and political leaders engage in the aptly named SOLT talks (a reference to the SALT talks between the US and the USSR). Over four episodes we revisit the main players of Mai-Otome and get to see how they fared after the big final battle.
Overall, Mai-Otome Zwei has a very slow, reflective mood. While there is an enemy to be defeated, and a world to be saved, even the protagonists
do not seem to be overly worried by the asteroid-induced crisis. And, given the history of happy endings in the Mai-world, neither should be the viewer. This is not to say that there is not a superbly animated showdown, but the emphasis of the OVA is on checking in with all main characters from the original series, not on the rather featureless antagonists. As an epilogue to Mai-Otome, the anime worked well for me.
Note: Mai-Otome Zwei is a follow-up OVA to Mai-Otome. Watching Mai-Otome first is crucial to understanding the story and watching Mai-Hime is at least helpful.