kill, die violent death
斃 centers on death by force or violence: killing or dying a violent death. The two given meanings are two sides of the same fatal event.
斃 combines 敝 (worn out, ruined) and 死 (death), suggesting death through destruction or collapse. The exact historical development is uncertain, but the component combination fits the meaning of violent death.
The top 敝 looks like something broken or ruined, and the bottom 死 is death. Picture a ruined body collapsing into death: 斃 is to die violently or to kill.
For ヘイ, imagine a violent death scene where someone says 'Hey!' in shock: Hey -> ヘイ, and the ruined body lies dead.