For as abjectly horrifying Tarn and the DJD were, they cared about Nickel. And Nickel cared about them.
Tarn gave her this phone with this prerecorded message on it in case she ever got into trouble. If I remember her interactions with the DJD, it was in general a sort of mutual symbiosis.
I like to headcanon that Tarn is a big fan of musicals and operas.
It’s one of his guilty pleasures that he tries to hide from his crew because “no why would I like anything made an inferior species”.
Imagine they run into someone on the list and he had to pause in the middle of an emotional part and the whole time that they’re torturing some poor soul he’s fighting to not break down into hysterical sobs.
It turns out one traitor likes the same ones that Tarn likes, and that one gets to live longer than the others so Tarn can have someone to talk about his interests with.
The rest of the DJD already know and make a game of intentional making references just to watch Tarn silently freak out. They grade eachother on how seamlessly they integrated it, timing and how Tarn reacted. Bonus points if the reference was a movement instead of words.
He lets the pet watch with him since it’s a dog that can’t judge him.