劈 combines 辟 (likely a phonetic component) with 刀 (knife), suggesting splitting or breaking with a blade. The exact historical development of 辟 is uncertain.
Meaning mnemonic
The top part 辟 looks like a complex object being forced apart, and the bottom 刀 is a knife. Imagine using a knife to split or break something open.
Reading mnemonic
For ヘキ, picture a heavy axe splitting a log with a sharp 'heki' sound: heki -> ヘキ, and the knife 刀 does the splitting.
