to trust to, send a message
俜 centers on entrusting communication to someone: trusting a person to deliver a message or act as a go-between.
俜 combines 亻 (person) with 甹, which likely contributes the sound and relates to conveying or sending. The exact historical development is uncertain.
A person 亻 beside 甹, a shape that suggests a message being sent out. Picture a trusted messenger carrying a sealed scroll.
For ヘイ, imagine the messenger giving a quick 'hey!' to get attention before delivering the message: hey -> ヘイ.