Yuutousei ja Irarenai! Majime na Mashiro-san ga Yankee Koukou ni Iru Riyuu

Mashiro Kanon is a simple and serious girl who attends a high school full of delinquents. Her only objective is to safely graduate but she has a secret only her childhood friend Tenma knows... for some reason, trouble always stirs up around her and somehow she always comes out of it unscathed.

(Source: Shogakukan, translated)