I figured it out, the final villain is copied straight from the Bible. Blackbeard will have 3 souls inside him by the end of the series, he represents the 3-headed devil from Dante’s Inferno. He also parallels god himself who is consisted of 3 equal beings, this would make BB ascend into divinity. This is why Xebec and Imu are introduced roughly at the same time (900+) — they are both the final villains.
The Father — Xebec
The Son — Teach
The Holy Spirit — Imu