Hmm! I'm fairly easy about whoever comes along for the trip - would it be better for Naoto to see something of how Phantom Thieves roll, even if the actual 'thievery' gets downplayed a bit in this situation, or for Matt to get a bit of dungeon time under his belt (though this isn't a 'we supply the Personas' dungeon, does he have any fighting gear?) or for Helena to just come meet someone who can talk tea varieties with her? It's pretty much a case of - who would make for good CR to start, or would get something from the experience?