Eternal Hatred.

His first move starts where the 6th step of weapon mastery ends and as such needs a lot more power than what he had. He had to supplement it with the power of the world. World power was forcefully infused into his body without having a body of law to contain it. It caused his body to crack. He went behind what he should be able to do. It is remarkable but it could also have led to his death.

His other reason for not using it is the lack of synchronization between his body, mind, and eyes. He needs the three of them to work in tandem to use the WORLD BREAKER but this world has placed a limit on his body and soul at 10%. 90% of his body and mind have been shackled preventing him from wielding his skill set properly.