If you train at the soils, just casting kahii level 1 will do, it heals 200hp/hit you receive and usually Soils won't reach you. Only the mantis will hit you from times to time and 200hp is more than their damage so you will never take damage and barely spend SP on healing. This way you maximize the SP you can use to kill monsters. Also at high int, its possible to 1 shot soils if you use the fire element.
I level my own soul linker at the soils and after trying many places I found it to be the most efficient for this class.
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair."
