Even though Musk couldn't practice any techniques, over the years he didn't forget to practice the Black and White Lotus skill. It was the only skill he could practice in this world and this surprised him, considering it was related to the soul.
As for what was possible, one shouldn't be shocked to know that the soul technique could indeed be practiced, by those with stronger souls, even if they were weak. The soul below the demigod realm has yet to take the form of anything, and in most cases, they come in the form of a physical manifestation of their true body at that stage.
Musk's true body even with his strong soul quality, reaching very frightening levels, couldn't form a physical manifestation of himself. In this way, the soul would be in the form of clouds. As such improvement was not difficult, and in this world, it was even more strict, as he couldn't exploit it for perception.