Within the depth-psychological corpus, ‘Sister’ operates across at least four distinct registers that resist easy unification. At the most fundamental level—developed most rigorously by Neumann and Hillman—the sister-image functions as a specific modality of the anima: proximate, ego-syntonic, spiritually inflected, yet erotically charged precisely through the incest prohibition that surrounds her. Neumann contrasts her with the ‘Mothers’ as a figure of individuated feminine consciousness, arguing she enables man to encounter woman as a separate ego-bearing entity rather than as a collective force. Hillman, reading against a merely reductive Freudianism, insists the sister-imago bodies forth the quest for inner wholeness, the desire to unite ‘like with like’ in the Jungian sense, and should not be collapsed into infantile wish. A second register—visible in Harding, Jung’s case studies, and Freud—treats literal sisters as carriers of familial identity-fusion, libidinal fixation, and regressive constellation, where sibling identification becomes a psychological obstacle requiring resolution. A third register, touched by Goodwyn and alchemical commentary, aligns the sister with the soror mystica of alchemy, a spiritual co-worker in the individuation process. Finally, structural-linguistic treatments (Benveniste) and mythological ones (Campbell, von Franz, Estés) chart the sister’s cross-cultural role in kinship taxonomy and narrative archetype. The productive tension throughout is between the sister as psychological image of inner wholeness and the sister as object-relational figure whose actual resemblance to the ego makes differentiation therapeutically urgent.