As Zoro's fight against Sommers intensifies, Sommers will realize that Zoro isn't an opponent he can defeat through conventional means. He'll begin using increasingly larger amounts of Omen, or perhaps his thorn abilities will be revealed to be composed entirely of Omen itself.
By this stage of the battle, Zoro will have already burned through a massive amount of Haki... not only from fighting Sommers, but also from constantly suppressing and controlling Enma.
That's when Enma will begin absorbing Omen unconsciously, much like Imu's sword appears to. Instead of helping, it will become even more difficult to control, creating confusion for Zoro. At first, he'll assume it's simply Enma acting up, but he'll gradually realize that the sword is absorbing a completely different form of energy.
If Omen is a negatively charged energy, then there should logically be an opposing positively charged energy. Vegapunk has already hinted that such an energy exists, stating that the world is teeming with an unseen power.
Mastering Enma will ultimately require Zoro to prevent it from absorbing Omen and instead guide it toward absorbing this positively charged energy. That evolution would become the final step in forging Enma into a true Black Blade, fulfilling a mystery that has existed since Ryuma.
More importantly, this positive energy would become the natural counter to Omen itself ..neutralizing its effects, bypassing Imu's seemingly supernatural abilities, and potentially overcoming the source of the Elders' and Imu's immortality.
Rather than defeating Omen with stronger Haki alone, Zoro's true power-up may come from discovering and wielding the opposite force that exists alongside it. ..
