gulf, bay, inlet
灣 centers on a curved body of water that cuts into the land: a bay, gulf, or inlet.
灣 combines 氵 (water) with 彎, which likely contributes both the sound and the idea of bending or curving, describing a curved inlet of water.
Water 氵 on the left and a complex right side that suggests something bending or curving: picture a winding coastline where water curves into a bay.
For ワン, imagine a calm bay shaped like the number one: one -> ワン, and the water curves into a single perfect inlet.