The Kikae dialect is a regional variety of Swahili spoken in the southern part of Unguja, the largest island of the Zanzibar archipelago. In this dialect, the morpheme -wa preceded by a subject prefix, which agrees with the subject in person or noun class, is used as a copula. This form is used in neither Standard Swahili nor the Kiunguja dialect considered prestigious dialects of Swahili. In this paper, I describe the morphological and semantic characteristics of this copula, which have not been observed in previous studies, and propose a possible grammaticalisation path of the copula based on its synchronic properties and typological evidence. The following three claims will be made: 1. the subject prefix -wa morphologically corresponds to the perfect form, but does not encode a prior event unlike the perfect form of other verbs. 2. The use of the subject prefix -wa copula is restricted to ‘predicational sentences’. 3. It is highly probable that the subject prefix -wa has grammaticalized from a locative verb