vomit, spit up
哯 centers on the forceful expulsion of stomach contents through the mouth: vomiting or spitting up.
哯 combines 口 (mouth) with 見 (see), likely suggesting the visible act of vomiting from the mouth. The exact historical development is uncertain.
The mouth 口 opens wide and you can see 見 the contents coming back up: vomiting.
For ケン, imagine a person named Ken who vomits after seeing something disgusting: Ken -> ケン, and his mouth 口 lets you see 見 the result.