Classroom of the Elite (2017)

S1E7 Nothing is as dangerous as an ignorant friend; a wise enemy is to be preferred.

Throughout the summer break, the introverted Horikita prefers the solitude of her room and her studies over socializing. However, her classmate Ayanokouji encourages her to join him and a few friends for a day at the pool, prompting her to step out of her comfort zone.