plural
plural refers to a wide array of experiences that can be summed up best by saying, "more than one person in a single body/head"
for a lot of folks it happens through DID (dissociative identity disorder), and often it can be caused by trauma especially childhood trauma
not everyone who is plural has DID or has their experience caused by trauma, though
for us specifically we think it was probably a result of neglect & abuse during middle childhood, which was when most of adrian's mental issues began, & extreme escapism into books and other media during that time
kin
kin refers to a wide array of experiences that can be summed up best by saying, "having a strong connection to an animal, mythological creature, or character"
most of the people who use the term kin specifically refer to having a strong connection with a character or multiple characters
the term originates, we believe, from the term "otherkin" which generally refers to the same thing with more of a focus on animals or mythological creatures
some people also use the terms "therian" & "theriotype" to discuss having a strong connection with existing or extinct animals, often mammals specifically
there are people who are very serious about their kin identities and people who are not very serious about their kin identities
(both are fine idk, we're not gonna get upsetti about how other folks relate to stuff 
)
for us specifically
adrian uses "kin" to describe character identities (like their namesake alucard) and "theriotype" to describe their connection to bears
&&
the rest of us feel that our identities are so closely related to being plural that "kin" doesn't quite describe then, but if our situation was a little different the term would probably be Correct