Mizuha/Relationships

Fushi
While Mizuha doesn't "actively" know or remember Fushi, she reacts to Aoki saying his name by gripping her left arm. All of Hayase's successors carried a knocker in their left arm, which indicates that she is related to Hayase's clan. When Hanna asks if she knows him, she answers, "No, not really... it just made me feel really nostalgic."

After learning the truth about her family, she decides that she wants to "obtain" him to become "truly perfect". With this, she follows the same goal as Hayase and her female successors. It's possible that Mizuha as well feels drawn romantically towards Fushi despite describing herself as a person fixated on logic alone.

Hanna
Hanna is Mizuha's only female friend. The two became friends in middle school. They seem like close friends, but Hanna is still somewhat awkward around her and doesn't think they're especially close. On the other hand, Mizuha wears the hair tie that she got from her every day. It's been hinted that she possibly may have romantically feeling's towards Hanna.

Yuki Aoki
Aoki has an obvious crush on Mizuha and says so openly in chapter 117: "A peaceful world is where your crush is in the club room" while Mizuha is there. It's unknown if she reciprocates these feelings. However, she says that she already has a crush on somebody in the same club as her. Since she spends a lot of time with the people from the occult club, it's possible that she likes Aoki.