Mizuki Koishikawa (コイシカワ・ミズキ Koishikawa Mizuki) is a member of DASH and an excellent pilot. She is Kaito Touma's partner in the field, who she often teases. But at the end of the series, she shows her love for Kaito. Mizuki can be impetuous just like her partner, both putting themselves in danger to carry out there misson. She joined DASH in hopes of meeting people from other worlds, and dreams of the day when all the people of the universe will come to understand each other.
While fighting a monster Grangon, Mizuki spotted Kaito near the monster and tells them to hold their fire until he left. After the monster was seemly destroyed, Mizuki met Kaito and told him he shouldn't have been near a monster, but Kaito told her he was protecting a boy and all that he wants to do is to protect people and be better than DASH, and left.
- In the 37th episode the theory that she is the descendant of Alien Saton emerged, but its truth is unknown.
- It seems that Mizuki knew that Kaito is Ultraman Max in the middle.
- In the manga version she is drawn in a dark personality, setting she dislikes Elly.
- Mizuki was meant to be named Akane.