Me & My Brothers Vol 5 (Manga)

Sakura's brothers are in an overprotective uproar when she becomes the boys' soccer team manager at a summer training camp and takes her team on a group trip to a theme park. They know she'll be alone with boys, and they don't want anything to happen to their precious Sakura! So they devise a brilliant plan to "sneak and peek" on her field trip, but if they're this nervous about her being left alone with members of the opposite sex, imagine how scared they'll be when she catches them at their brotherly meddling!