to request, to ask a favour of
浼 centers on making a request or asking a favor, often with a sense of entreaty or seeking help.
浼 combines 氵 (water) with 免, which likely contributes the sound. The exact historical development is uncertain, but the character is associated with the idea of requesting or entreating.
The water radical 氵 beside 免 suggests a person bowing low like flowing water to ask a favor. Imagine someone humbly requesting help, their posture as fluid as a stream.
For バイ, picture a person bowing deeply and saying 'bye' as they make a heartfelt request: 'bye' -> バイ, and the bowing motion matches the humble asking.