Your post on the fictionkin fictive difference made me wonder – what about fictives who are also fictionkin? As in, they remember past lives in the same way any fictionkin does, even though they have a main/current form similar to a fictionkin’s current life. But maybe that’s a soulbond thing? Since I always heard that fictives were specifically related to alters who are fictional, and soulbonds can come and go as they wish and aren’t necessarily a part of the host.
I won’t take a stance on whether alters can be fictionkin, as alters are specifically DID related and not something I am qualified to discuss.
However, soulbonds, and other types of headmates can certainly be fictionkin, and I have known several who claimed to be. These were headmates who had a concrete identity to begin with, and then discovered that they were fictionkin of another character, generally from another life or universe.