Mizuho came to Earth to monitor the planet, but inadvertently she was seen by Kei as
she was just landing on Earth. Although she did not trust him at first, she started to become attracted to Kei and eventually falls in love with him after they shared secrets about their past to one another. Kei and Mizuho are found in a locked storage room by Kei's uncle and the principal ofthe school, his uncle impulsively tells the principal that Kei and Mizuho are married. Later, Kei and Mizuho do get married, though only the paperwork is done while there was no official ceremony.
Pursued a romantic relationship with Kei, but was unrequited. Towards the end of the series discovered her affection for one of her teachers, Yamada. During the anime this bamboo relationship is only ever hinted at, but in the OVA special Ichigo taunts her about having sex in his room triggering a flashback. In the series itself, Yamada is confronted by the principal about him seeing Yamada and a girl from their school walking together.
During an accidental visit to her hotel room by a sleep-deprived Hyosuke, in
which he mistakenly climbed into her bed, she awoke from a lightly inebriated slumber and claimed that he had appeared to her in a dream which now seems to have come true. She then sweetly confesses her love for him and proceeds to seduce him. The two become inseparable and are seen together throughout the series, to the point of being seen exiting a love hotel together in the OVA.