This article discusses a potential background of the emergence of prepalatal initials, which are expected to be denti-alveolar counterparts as an ordinary sound correspondence, attested in the rGyalthang subgroup of the Sems-kyi-nyila group of Khams Tibetan, spoken principally in Shangri-La Municipality, Yunnan Province, China. It clarifies that the condition of the phenomenon is related to either a case that a given sound precedes /i/ in a synchronic aspect or a case that a given sound precedes a Literary Tibetan (LT) vowel e. The article further analyses that LT e corresponds to *jə in a proto-form (proto-rGyalthang), which means that /i/ and /j/ effect the development of the initial from denti-alveolars to prepalatals. This analysis can be supported by a parallel case that LT o can correspond to *wə in the proto-form