This page explains how to recruit Miki in Chrono Cross: The Radical Dreamers Edition.
Miki is a dancer who performs for the Magical Dreamers, alongside Nikki.
How to Recruit
To begin recruiting Miki, you need to complete the sidequest to save Marbule. This sidequest is only available if you spoke to Nikki after defeating the Sage of Marbule and before the Tower of Geddon.
Upon completing the sidequest, return to the S.S. Zelbess and enter the diner below deck. You’ll find Miki by the balcony, ready to be recruited.