Bì is odd among IA first person singular pronouns in that it doesn& #39;t descend from an oblique Skt. form with m- (H. main, B. ami, Mar. mī) nor the direct form aham (Kalasha a, Khowar awa). Some etymologies have been proposed including a native development of the root भू "to be."
Masica proposes that bì derives from the first person plural pronoun vayam. This would be a very strange development but there are parallels for it. Ex: in some Hindustani dialects the 1st person plural hum is used as the singular.