Also they involve girls (or dolls) with magical power, although this isn't specifically the case with Sekirei (one of them is a guy, another one doesn't know his/her gender), most of them just are.  The powers a "focused" (eg elemental") and unique for each of the characters.  Action scenes with fancy effects, all of them seem to have some ability to fly and some others.  And they all seem to have some "big boss" guy spearheading all the competition.  Akikan and Sekirei involve some teaming/factioning, but Mai-HiME and Rozen Maiden is mostly a free-for-all (although they had initial cooperation).  There's some "love" involved, although that's common across shows which feature major female characters; and all seem to involve a harem.
That's probably main things I see common across all of them, although I'd personally say the execution is somewhat a bit different between them.
This is really a vague plot element IMO.  Survival of the fittest exists in many places, whether it's simply a tournament the main character has to win or whatnot.
How many shows involve some drug/crime gang doing something evil and being hunted down by police/investigators again?

(This post was last modified: 08/06/2011 04:41 PM by ZiNgA BuRgA.)