Gonzoron I can probably tell you a tiny bit of what we saw in Black Dice Societies streams, Nepenthe is Isolde's sentient sword. Again take a grain of salt but the DM has said he's been trying to play it as close to the book as possible again to showcase what he could before it releases. Nepenthe seemed to be able to show a player a vision, and while I'm not sure may be causing Isolde to be very judgemental towards those who are "guilty". Making her an ally for sure, though if you have a blackened past you'll want to be careful around her sort of thing.
Other than that I don't think we got much more about Nepenthe, though I could go back and rewatch those parts. Needless to say the party left in haste on a mission they got from Isolde, and why they left in haste is because the GC decided to visit one of the players seeming to stop time to have a brief and private conversation with the player. (I'm assumine this is DM Fiat for the GC stopping time) Needless to say when the Player ended up trying to be forth coming about the event the DM rolled to see if she might recognize it was the GC, and almost immediately she assumed the PC to be working with the Caller, and was seemingly fighting with herself to see reason. (My Guess is that sentient sword wasn't helping matters.)



