親子別

• o at its mouth
• + ya shore, bank
• + kor have
• + pet river

Proponent: zenibako_trek（小樽銭函地名歴史研究会） (zenibako_trek (Otaru Zenibako Place-Name and History Society))

The author raises the objection himself: every river has a shore at its mouth. The point is taken to be the Raiden mountain road. That road runs some 10 km over the hills and comes down to sea level at one place only, where the track from Asahi-onsen descends by the Oyakobetsu. Asahi-onsen sits on the upper Yūnai River, but the Yūnai is steep-sided, so the way down went by the neighbouring Oyakobetsu. On that reading the name marks the river whose mouth the descent reaches.