Tearing the Demi God might have looked easy but it had required meticulous preparations. Draining the Demi God's energy was only one of many conditions that had to be met.
Once the Demi God's energy reserves were below a certain threshold, the Death and poison curse power inside Lanester weakened his body. Michael focused Death and poison curse power on the Demi God's neck and shoulders, further weakening these areas. The Divinity within Death Call was drained when the Demi God was weakened enough to unleash the Power Authority.
He used the Divinity accumulated within the Primordial Vessel in one go, pushing his raw power to a new all-time high. Lanester tried blocking Michael's attack, but his body was torn apart before his hands could tear through Michael's chest and pierce his heart. The Demi God had attempted that with a last-ditch effort, but a double-layered Imperial Barrier covering his chest was enough to block the attack.