Mayonaka no Ariadone

From StarryHeaven:

When you have worries, is it about whether or not you are short or about your new class? Those were the problems that normal high school student, Chiyoko, faced. However, one day she meets her childhood friend Chiharu and Chiyoko’s world changed. But when Chiyoko stumbles her way into a secret underground high class club, she is surprised to find the truth…