Now that we've come this far, I can now say this without being a spoiler. Harukara is Azusa's best wingwoman.
I mean, think about it. After Harukara joins, look at Azusa's harem member:
- Beel: joined because Harukara fucked up
- Rosalie: Joined because Harukara fucked up
- Maou: Joined because Harukara fucked up
- Fruitcake: Joined because Maou, who joined because Harukara fucked up
So, all of the member in Azusa's harem after Harukara joined are all because Harukara fucked up, one way or another.