Saki Kawasaki

Saki is Hachiman's classmate who seems like a delinquent, but wants to make friends deep down. She cares deeply for her brother as she hid her name and age to work in night-shift part-time jobs in order to pay school fees and reduce her family's load. After her brother asked help from the service club, the service club eventually followed her to her workplace and found out her motives behind working night-shifts, she stopped working after the service club suggested her to aim for a scholarship instead.

Source: Yahari Wiki