Athena Tennousu

A-tan, Alice, 天王州アテネ

Athena Tennousu is a character from the manga series and has not been featured prominently in the anime. Her parents are believed to be missing or deceased as she lived alone. She was Hayate's first girlfriend, whom he met 10 years ago when he was young. He affectionately called her "A-tan" at that time.

Spoilers:

In the manga its shown that she has feelings for Hayate despite being away from him for 10 years. Though when she meets him again she lies to him that Her family owns Hakuou Academy, and she is the board chairman of the school. In the 4th season she appears more frequent and becomes one of the tenants at Nagis dormitory.