Both Theo observed each other's movements. Since they were the same person, their train of thought was similar. Even with Theo's brain and experience, it was still hard to outsmart his original self.
So, he needed to find some weaknesses to exploit. There was one big difference between him and the original Theo. He had an insurmountable amount of experience, while the original Theo didn't. This was the advantage he could take advantage of to defeat him.
With this thought in mind, Theo moved forward while gathering his energy all around his body.
The original Theo also did the same thing. Once they were about to clash, the original Theo pointed his hand toward Theo.
Soul Poison.
Theo's eyes flashed as he threw himself to the side. According to the system, the Soul Poison directly attacked his consciousness which could be considered his soul. Although he had some training with the Death Eyes, he wouldn't underestimate Theo's original skills.