Kuroneko-kun wo Kainarashitai

Mineko Haida, the third-year chief of the school disciplinary committee, is hard-nosed and strict, but she turns into a big softie around cats. One day, she found Yuu Kobukuro, a delinquent junior student, playing with a cat. Mineko was so taken by Kobukuro's resemblance to that black cat, that she was thrown for a loop.

(Source: Natalie.mu)

Note: The original one-shot was serialized for winning the grand prize in the "Betsuma, Cat Slot Available" contest, for "deciding the cat mascot that best represents Betsuma."