Where does “*ʃe²” come from?

*ʃe² (Proto-Loloish) comes from Proto-Lolo-Burmese *səj¹, from Proto-Sino-Tibetan *sij.

Ancestry of “*ʃe²”, step by step

Step	Language	Word	Meaning
1	Proto-Lolo-Burmese	*səj¹	—
2	Proto-Sino-Tibetan	*sij	—