In Persona 4: Arena, there are six Navigators (essentially, announcer voice packs) that are available as optional paid DLC. In the Marketplace description for all six DLC items, however, it states that "skilled players can unlock this content by playing the game."

I know of the following confirmed methods so far:

Teddie: Clear Story Mode completely
Mitsuru: Complete 100% of one character's challenges
Nanako: ???
Aigis: ???
Fuuka: ???
Yosuke: ???

How can I unlock the remaining Navigators?