Ryouko Arigase

One of Koizumi's friends, Ryoko has long purple hair. She tends to remain calm, despite whatever is going on around her, she will usually put on a face to match the situation, as well as saying something to go with it. In manga, she is considered as a Venus with purple hair due to both well endowed shape and her sexiness. In the manga she also has a boyfriend named Konoe, a friend of one of Saji's friend's older brother. His shyness results in her usually taking the initiative in the relationship, which seems to suit her just fine.

She has a habit of somewhat discreetly supporting Saji and Koizumi's relationship, putting them in compromising situations and making various short comments concerning her take on what Koizumi really means when the girl expresses frustration or hatred for Saji. At one point in the manga she counseled Saji (who was trying to learn from Konoe how to control himself better) to be himself, as that is what Koizumi likes even if she won't admit to it.

(Source: Wikipedia)