Koubaibu no Onee-san

The young cafeteria lady, who often wears a kind smile while making lunches for all the school's numerous students, who affectionately call her Onee-san (おねえさん?), a respectful word for sister. She can be subject to a dark streak of anger when her food is damaged. she tends to con the customers and students into buying faulty merchandise or working.

(Source : Wikipedia)