Maru Sankaku Shikaku

In the spring of Chitose's 1st year of middle school, Mika, who shares the same last name as Chitose, is transfered into her class. Mika is pretty, quiet, and sticks like glue to Matsuura whom Chitose has unrequited love for. Chitose is bothered by the relationship between Mika, who won't make any female friends, and Matsuura, who is treating Mika kindly. Meanwhile, it's been set that Chitose is going to transfer schools-!?

(Source: Eternal Heart)