Hiyama Hikaru
Hikaru is not the sort that gives up on things easily. She is persistent and stubborn, and usually won't rest until either she gets what she wants or her Darling convinces her to pursue some other thing. Kyousuke is her Darling, and had always been so eversince she witnessed the most amazing basket ball shot ever (sitting down, all the way across the court, nothing but net... aided by a little ESP). With this unwitting act, Kyousuke has unintentionally gained the complete and utter adoration of Hikaru. Thus began the Orange Road Triangle.
Hikaru was quite a tough girl like her close friend Madoka until she met Kyousuke. The meeting transformed her from rough-and-tough street brawler to a dandelion mush that chirps "jepi!" and "Da-rin!" whenever she's around Kyousuke, who she always calls "Da-rin". Her devotion to Kyousuke is immense; she would do just about anything for him. Unforturnately for her, he had already met Madoka. Kyousuke does harbour feelings for her, but they're mostly of the brother-and-sister kind.
If Kyousuke had never met Madoka, then it is almost certain that Kyousuke would be Hikaru's. This is best symbolized in a scene in the tv series where if Kyousuke didn't go to the right side of the fountain in the park with Madoka, he would have ran into Hikaru on the left. The blind devotion that made Hikaru oblivioius to what's going on between Madoka and Kyousuke, coupled with Kyousuke's indecisiveness and Madoka's inability to openly express her feelings, made the triangle last as long as it did.