Cultivation consumed far too much time. It could easily take decades or even centuries. Although Nawaki possessed advantages such as the Spirit Transformation Technique and the Rinnegan, allowing him to cultivate relatively quickly, that speed was only relative.
Originally, Nawaki had thought that, having reached the pinnacle of Yin Release through the Eternal Mangekyo and experienced the sensation of leaving the body early through the Spirit Transformation Technique, he would have no bottlenecks and should soon be able to condense his Yin Spirit. But he later discovered that his foundations were far from sufficient! Condensing a Yin Spirit required immense spiritual power, while the Stellar Art Nawaki had created by combining the Mysterious Peacock Method with the Microcosm was, due to incomplete theory and no knowledge involving meridians and acupoints, at most a basic cultivation method. Its cultivation efficiency was extremely low. On top of that, he had no pills to assist him, so his realm advanced at a painfully slow pace.
By Nawaki's estimate, it would take him at least several decades of arduous cultivation to condense a Yin Spirit on his own.
And after condensing his Yin Spirit, he would still need to continue absorbing natural energy to cultivate Sage Art chakra, slowly strengthen his physical body, and completely unify Yin-Yang Release before he could obtain a Sage Body and fully enter the realm of the Six Paths. Who knew how much more time that process would take?
Reincarnating into any world was a technical matter. Hamura and Hagoromo, for instance, had been born with Yin-Yang Release and Sage Art chakra. As long as they cultivated step by step, they would face no bottlenecks before reaching the Yang Spirit realm. Moreover, they could absorb natural energy from the very beginning, making their cultivation ten or even a hundred