Ritsuko Iwashita

Ritsuko Iwashita is a student in Class 2-B in Fumizuki Academy and is good friends with Mayumi Kikuiri.

In Volume 1 it seems she is strong at math, but was still quickly defeated by Mizuki Himeji. In Volume 2 and the Matsuri OVA, she and Mayumi fight Akihisa Yoshii and Yuuji Sakamoto because of technical difficulties during the Summoned Being Tournament, but even with a 116-point lead on Akihisa, she loses due to his Shoukanjuu's agility and his teamwork with Yuuji.

Her Summoned Being differs the most amongst the series' media. In the manga adaptation, it wears a black ninja uniform and wields a katana. In the anime adaptation, it wears Western-style armor and wields a sword. In Episode 2 of the Matsuri OVA, it has bunny ears, wears normal girls' clothing, and wields a giant hammer.

(Source: Baka to Test Wikia)