>>529340758
>who becomes a Phantom Thief
Yesn't.
Her PT form is a Phantom Idol.
It's the Wonder's (the MC) cognition of how he thinks Kayo Tomiyama would look like as a Phantom Thief, clearly influenced by a certain picture she shows to him early on.

>Is it possible to romance her?
Nope. She's married.
She does have a confidant though.