[Kazu-kun]

Originally Posted by chaosprophet

Spoiler for ep 10:

Based on her conversation with the former Mii-chan the 5th, I'm wondering if she plan to being the Centar Nova Position back in hopes of being able to discover then what happens to one so she could save previous Acchan somehow. But if that was the case why wouldn't she just use Yuuko?

I thought the same.

Spoiler for ep 10:

This episode really gave me the impression Tsubasa would go as far as to use/sacrifice other girls to find out how to save Acchan.

As for why she didn't use Yuuko. It seems clear to me Yuuko doesn't have the sort of radiance needed to become a Center Nova. I assume that's why she's so interested in Chieri and Nagisa.