Ren kept on swinging the branches around as if they were swords. Even though his main weapon was a scythe, Ren felt so enamored by the swordsmanship he saw in his visions that he couldn't help but wanting to practice it. The swordsmanship he saw felt so familiar, so he was able to copy it with memory alone.
The swordsmanship Ren used when he was a demon lord, focused solely on attacking and its defensive capabilities was abysmal. The reason why Ren created such a swordsmanship was because he thought it would only take him one hit to kill his opponent, and even if the opponent survives the first strike Ren decided that the best defense was a good offense. So Ren's style had little to no defensive moves.
