Duan Lingtian had a very simple "method" in mind. Once he returned, he would find an opportunity to try and improve Kecier’s innate spiritual root.
Kecier’s current innate spiritual root was a "deep purple" one, which was already considered top-tier in the Dao Martial Saint Land. If, while trying to improve her spiritual root, he discovered that there was still room for further growth, it would mean that the "deep purple" spiritual root was not the absolute limit! Innate spiritual roots could indeed be further improved.
"I really want to go back soon and test it with Kecier... to see if the 'deep purple' spiritual root is truly the limit!"
Chapter 2233