Missions of Love Vol 4

From the Kodansha edition

Now that she's back after a long sick leave, Mami Mizuno, the girl every boy in school has a crush on, never leaves Shigure's side. Never, that is, except for when she's pestering Yukina. She claims to want to help Yukina win Shigure's heart, but what is she really after?

Source: Anime News Network Encyclopedia