The nipples are censored because this is a big ol' tease.
These are taken from the blog postings promoting the doujin "GIRLS ONLY!!!", which Tehen is selling -- http://www.toranoana.jp/mailorder/cot/pagekit/0000/02/48/0000024842/index.html has a couple of the same preview pages without the censorship. Sort of the doujinshi equivalent of the steam in TV anime onsen scenes that gets taken out for the DVD version.
