Basically, my players have an NPC who is severely traumatized by events that have taken place (it may be their fault… but this isn’t about blame, this is about healing)
What would you ask them to roll when trying to help with the mental health of this NPC? Narratively, I’m fine with them spending time doing talking therapy in sessions with the NPC, but I don’t know how to do it mechanically. I’ve thought that Medicine and Leadership are both relevant, but neither seems like a good enough fit.
We’ve used Medicine in the past for diagnosing the psychological issues of NPCs. For getting them to do things to improve their situation, Leadership can be appropriate, or just Charm for being a friendly influence. It kind of depends on how much you want this to be a part of your game. That you are asking the question at all suggests that the PCs feel compassion for the NPC and that the NPC is important to them, so I wouldn’t hand it with just single roll.
What I’'ve done in the past for therapy is have a decreasing difficulty check with each difficulty level having a set number of successes to continue on to a lower difficulty. Each time the party spends time to do therapy a check is rolled, the skill used for the check is entirely dependent on how the party is conducting therapy. This results in charm, leadership, medicine, negotiation, education, and xenology being able to be used. Anything that the party does to make the traumatized more comfortable will add boost die, and anything that might remind the patient of the incident adds setback die. Similar to how crits get healed I only allow 1 therapy session a week, and any things that happen between the therapy sessions can impact the next therapy session in terms of boost/setback.