In 866, however, the Otenmon incident occurred, in which KI no Toyoki who was Natsui's half-brother with a different mother was arrested as a main culprit, which resulted in implicating Natsui, who was thereby removed from the position of the Governor of Higo and banished to Tosa Province.
しかし、貞観8年（866年）に応天門の変が起こり、異母弟の紀豊城が首謀者の一人として逮捕されると、夏井もこれに連座、肥後守の官職を解かれて土佐国に配流となった。