In the past, Aksai had only used the Brain Bonsai Formation as a support tool to help him comprehend complex concepts.
The Brain Bonsai trees were originally something he had obtained from a Bloodfiend Art user. Later, he acquired another, more detailed Bloodfiend manual.
Furthermore, Aksai had come across a collection of books and scrolls related to the Bloodfiend Art after defeating the Lakir clan's Foundation Building old ancestor. After the entire Lakir clan decided to leave the Dadangar Subcontinent behind, Aksai could be said to be the only user of the Bloodfiend Art in the region.
Of course, the Spirit farmer didn't let this knowledge gather metaphorical dust. Instead, Aksai delved deeply into it, forming new ideas inspired by the concepts outlined in the manuals.
Using these ideas, he refined the Brain Bonsai trees even further, and from that, the Brain Bonsai Formation was born.