Volume 1 Introduction: Lillian Girls' Academy is a private school for purely cultured maidens. In order to carry on the pure and correct school life, a system called "sisters (suru)" exists in the upper school. After the students pledged to become sisters through a ceremony in which they received a rosary, the older sisters would mentor the younger sisters. Yumi, who had not yet had an older sister when she entered the upper secondary school, was suddenly declared a "sister" by Sachiko, a sophom...
If you've seen the anime, there isn't really anything interesting in here that wasn't already there. Otherwise it's a perfectly fine school trip story. Since it's Italy there's tons of Italian vocab (of the you'll probably recognize this if you know about Italy variety), plus some 和製英語 & broken English. There's also tons of food mentions, so be prepared in case it starts giving you food cravings. There is a mystery involving Satou Sei that adds a little intrigue, and it's nice to see Yumi & Yoshino group up with Mami & Tsutako during the trip. There is a bit of discussion between Yoshino & Yumi about sisters and rosaries - but it doesn't really add much to what we already know.
I'm looking forward to getting back the main story finally, in the next volume.