Story: There isn't any story really, the majority of episodes consist of one girl coming home from school, worrying about something like periods or her breast size, and then her older sister telling her her own opinions and stories about all sorts of sexual things, what she discusses with her friends whilst groping her big breasted friend at work. It was amusing the first couple of times round, but it lost its pizazz and I soon dropped this show, realising it didn't really have much to offer. I began to feel quite a twerp still watching this anime.
Animation: Even for 1998, this animes animation isn't that good, the blurry images and bad audio didn't do the show much justice, and the characters moved quite oddly making them not seem very human.
Sound: The sound in this isn't very super either, not much music is actually used, just a few irritating jingles every now and then when a conversation about breasts kicks in. Best to watch this on low volume.
Characters: There isn't much character development in this show. I felt sorry for the big-breasted woman at the blonde sisters workplace, getting constantly groped by her friends and teased about her boyfriend, but other than her I didn't see much about the characters. But then again since I only watched 8 episodes I didn't give it much chance to progress with the other characters, so I can't properly judge.
Overall: This is only for teenage boys, who want to hear girls talk about periods and condoms and some such other sexual thing, or I suppose for girls who want a little bit more knowledge about sexual things like that and don't just want to Google it. Momoiro Sisters is for a limited target audience, thats for sure.
A pleasant, funny anime series whose only fault is that it is too brief. Great op/end songs and fun all around. For adult audiences.