Shiritsu Horitsuba Gakuen is an omake made by Clamp for Tsubasa Chronicles and it's sister manga xxxHolic. The series revolves around in a school called Horitsuba Gakuen (Holitsuba) with its teachers and students. The main characters are also the characters who stars in Tsubasa Chronicle and xxxHolic.
The characters include Syaoran(Real and Clone-but stated as twin brothers), Sakura, Himawari, Watanuki, Doumeki, Mokona(Soel) and Mokona(Larg) as students. The teachers include Fay(chemistry teacher), Kurogane(Gym teacher), Yuuko(Literature teacher, also the chairwoman) and Yuui(Home Economics teacher).