@Ray:I overall agree
Mari is what Anno and Gainax promise, fan service
The issue isn't her bust size persay, but that she acts and looks similar to a mid-teenage girl like the others, yet has far larger breats and booty compared to Asuka or Rei or the norm, thus voluptuous fan service lol They emphasize her knowing this and the jiggle as they move *drools alittle*.
I would also say Mari is the voice of the audience, especially the veteran of Eva audience. She is content and matter of fact about all of it, as we would be knowing what we know, thus perhaps showing she knows more than she lets on... or is a 4th wall break waiting to happen.
Sadamoto might have been going for the yuri thing in his manga, debatable, but all we know of Mari is she is a secret personnel outside of SEELE's agencies, super knowledgeful (and almost a Mary Sue, Rei did out do her against Zereul as mentioned), and is attracted to LCL and most likely Shinji. Beyond that, she is a mystery fan service character and not really important... not yet at least. In fact,
she, more than anyone but Shinji is probably what is holding Anno up in deciding where to go for the 4th film.
Prediction, she dies for Shinji in the fourth film and probably...hopefully, at least gets naked to stop wasting our time lol Also, maybe she will take Shinji's virginity this time, or turn out to be an angel, who knows lol Mari is not of the trinity of girls after all.
Mari's number one purpose is merchandising. If you like voluptuous teenage appearing chicks, Mari is it. If you want Milfs, Misato or Ritsuko...maybe Naoko too lol If you want petite and a girl who needs you and makes you feel needed highly, Rei. If you want Tsundere and such things associated, you want Asuka. Simple really. If you want elegant milf, you want Yui. Simple. Male demographic, male author, male audience and desire as the primary= $$$$$$$$(think yen here granted lol).