User blog comment:MrSolomon/MGQ Fanfic: War of the Seraphim/@comment-7475345-20150505073139/@comment-2037710-20150506185229

The only time a spirit manifests herself in front of everyone is in Sabasa's jail with Amira (or it could be Amira using her fourth wall powers or stuff :D...). Everywhere else is just only Luka talking to them in his mind or Alice overhearing Luka.

New Game+ by Ecstasy did make the spirits physically interact with Luka's other companions, though. So just do whatever you want.