[[WMG: What does pigtails and tsundere has to do with anyway?]]
* The point is that it adds in more "[[MoeMoe moe]]" traits, and therefore is more attractive. One person online mentioned that adding in [[CatGirl kitty ears]], [[GlassesGirl glasses]], and a [[MaidOfMoe maid uniform]] or SailorFuku would make the ultimate Zettai Ryouiki.
** The reason is that Zettai Ryouiki is more commonly seen on Tsundere characters along with the pigtails such as Rin Tohsaka of ''FateStayNight''. Tsundere characters alternate between hot headed and nice which is a trait that is commonly attributed to cats, which is why adding cat ears is considered moe. I have no idea about the rest though.
* The idea of of this trope is to highlight innocent sexuality, and pigtails are representative of youth (see GirlishPigtails), which highlights this further. Not sure about the tsundere aspects, but it may be beacuse tsunderes are very child''ish'', thus further highlighting that innocent, budding sexuality. But take my word with a grain of salt, I'm no anime fan.
* It may be just a [[FollowTheLeader trend]]/[[MemeticMutation meme]] started by [[FateStayNight Rin]]. Unless, of course, it appeared earlier than that.
** It's a lot older than that.