But what is soulbonding?

Demonic possession with the besties!!
We'll get back to you with a personalized essay at some point, but for now, here's a few links!

Pluralpedia definition. / Fanlore definition. / FromFiction compares soulbonding with other forms of multplicity.

Web archive of an FAQ about soulbonding and 1999 ancedote about soulbonding from the same source.