Yes, there is a term for an alter in Dissociative Identity Disorder (DID) that is not a fictive introject: "anautogen." An "anautogen" is an alter with a unique identity and personality that is not based on any existing character, real or fictional. These alters are entirely original and do not copy or borrow characteristics from external sources. Instead, they emerge as distinct identities from the individual's own psyche.
It's important to note that the experiences of individuals with DID can be highly diverse, and their alters can take on a wide range of characteristics and roles. Some alters may indeed have appearances or traits reminiscent of fantastical or storybook concepts, while others may embody more conventional human-like qualities.