Kaori was a young girl who came to attend Miator starting off in her first year. Ever since she was young, Kaori has been physically weak due to an affliction which remains unnamed, but apparently affected her breathing and possibly her heart. It was due to being this weak since birth that she spent most of her elementary school years at home, too sick to attend. She had a placid personality, and dealt with her condition with surprisingly good grace.
Upon arrival at Miator, she was entrusted to Miyuki and Shizuma in order to look after her and make sure she had a worthwhile experience while at the school. Eventually, Kaori and Shizuma formed an intimate relationship, which is why when Shizuma entered to become the next Etoile, she chose Kaori as her partner. However, by the time they both had become Etoile, Kaori’s body had deteriorated too much and before long she died, leaving Shizuma with a broken heart. Kaori apparently anticipated some of Shizuma’s response and left her a letter, which Shizuma is very late to find.
Note: While she’s dead from the start of the series, we don’t learn this until July 3, 2006.