When Mizuho was younger, he had very little self-confidence and in effect often would follow Mariya around, depending on her as his closest childhood friend. Additionally, his mother died from an unexplained illness when he was younger and one of her last requests to her husband, Mizuho's father, was to not force Mizuho to have his hair cut until after he had grown up. Mizuho explains this was so that he would be free to make his own choice of what hairstyle he wanted later on, and obviously he kept it, thinking it suited him best.
Mizuho's had to use the surname Miyanokōji, his mother's maiden name, in order to enter into the school; his actual surname is Kaburagi (鏑木). The Kaburagi family's biggest rival is the Itsukushima family, both of which are very well-endowed in terms of money and power. Mizuho didn't realize it at first, but Takako is a member of that Itsukushima family. Despite this, Mizuho doesn't see her as a rival and enjoys her company very much. In fact, they share Japanese history class together and sit next to each other. They often talk to each other during class by either whispering or passing notes.