Minamo Katsura

Minamo is Seina's little sister. She is physically very weak, though this is hidden by her constantly playing pranks and general acts of mischief (this has included making a mess of the Gokujou Seitokai's hostel and throwing Nanaho's foreign-imported teddy bear into pouring rain). She likes doing scripts and drawings and was the one behind projects such as the Gokujou Seitokai card game, featuring the members of the student council, and the (poorly received) play "Space Alien." Even though Minamo has a weak heart, she doesn't want others to feel pity for her, causing her to constantly push herself to the extent of danger to her health.

(Source: Wikipedia)