Mikoto Tachibana is Enkyou's daughter and Wataru's mother. According to her memories, Nagi's father resembles Hayate. It is revealed in Chapter 206 that she was good friends with Yukariko Sanzenin but according to Nagi, she went senseless after Yukariko passed away, thus relying on gambling for a living. (Source: Hayate no Gotoku! Wikia)