Fujiwara-kun wa Daitai Tadashii

The heroine Hitsuji is nicknamed "Kigurumi-chan" by her surroundings. While she is friendly with everyone thanks to her easygoing personality, she is distressed about not being treated as a girl. She's always had an unrequited love for her classmate Touya, who always quarrels with her. One day, the number one popular boy in the school and the student council president Fujiwara-kun suddenly gives her the new nickname "Mojako."

(Source: ShoujoHearts)