Yuki Hatoba

She was the first victim to have her heart's egg hatched into a X-Character.

Her egg was "hardened" due to her worring about moving to America

and having to face changes at which point Nikadou transformed it into a X-Egg.

[Spoiler] In the end, she was able to face the changes and moves to America.

Yuki's Guardian Character is dressed in a teacher's outfit. She is also very good in English. [/Spoiler]

(Source: Wikia)