Soon after their return, Kyawswa I came to power in 1344,[3] and appointed Yan Naung governor of Prome (Pyay), a strategically important region on the Irrawaddy.
Prome and its neighbor to the east Toungoo (Taungoo), the two southernmost vassal states of Pinya, practically became independent in the late 1350s when the central authority waned precipitously.
He apparently never supplied his share of manpower to Pinya in the latter's war effort against the Maw Shan raids either.
Yan Naung stood by as Thado Minbya attacked Toungoo, Taungdwin and Sagu, the vassal states to the east and north of Prome in 1365–67.
[6] Yan Naung's support helped Swa secure the allegiance of Sagu and Toungoo.
[7] Pyanchi understood the proposal of marriage to be the first step toward joint rebellion against Ava, and came to Prome with a small battalion.
[10] Nonetheless, Swa was pleased with the ambush, which avoided an outright rebellion, and upgraded his brother's status to viceroy.