Essek is someone who really prides himself on his mind. I want him to get feebleminded during some kind of attack. Maybe during an official something with his Den? And the Nein were brought in cuz they're technically wards of the Den or something? (they do live in one of their houses, if I remember correctly)

+Essek immediately latches onto the Nein, staying close to them and clinging to them
+This includes Beau and Veth, which surprises them given how they were questioning his loyalty so much
+He avoids his family actively, especially his mother, not recognizing them as safe to be around while he's feebleminded.
+Shadowgast being involved in some way (background or unresolved tension is fine, but if they're already together I want cute stuff! Gimme hand holding and soft kisses!)
+Essek is healed in the end, but everyone does end up knowing where his loyalties truly lie

If one wants to go a bit angsty I could see his Umavi disowning him for choosing this mishmash of outsider mutts over his own den, but it's just one possibility. I can see this going a lot of different ways.

---Permanent character death, bathroom stuff, smut involving Essek while he's still feebleminded