Ubukawa - Hajimete no Kare ("Very Cute~ First Boyfriend") by Nao Doumoto 5 volumes-completed
Uri is hardly noticeable at school. She then learns that her father is going to marry and she'll have an instant stepbrothers who also goes to the same school. The flow of the story is so-so but it's not your typical stepbrothers plot. Like Rakuen Danshi, I'm attracted by how the mangaka draw her bishies!