Since I'm bothering to tag her, I might as well mention here that the doctor popped up before in the full version of the EX chapter from a good while back. Her name's Azuma Chitose, and she's Mihari's senpai who worked with Mihari to make her gender-bender drugs. She has connections, and is probably the reason why Mahiro can even attend school again. We barely know anything about her right now, so it's good to see her finally appearing in the main story.

Nazdrovie said:

Since I'm bothering to tag her, I might as well mention here that the doctor popped up before in the full version of the EX chapter from a good while back. Her name's Azuma Chitose, and she's Mihari's senpai who worked with Mihari to make her gender-bender drugs. She has connections, and is probably the reason why Mahiro can even attend school again. We barely know anything about her right now, so it's good to see her finally appearing in the main story.

As soon as I read the translation on this page my first thought was that she was related to Mihari in some way, turns out I was right

Nayuta is connected to Mihari's sempai: Confirmed.

Speculation: Nayuta is, like Mahiro older than she appears.