Kuzuha Togashi

Kuzuha is Yuuta's younger sister who is in the first year of junior high school. She knows Yuuta very well, especially how he acted during his Chūnibyō days in middle school as Dark Flame Master, though she always considered him embarrassing. Kuzuha got used to her older brother's delusions since she was young.

(Source: Chuunibyou demo Koi ga Shitai! Wiki)