Enhanceable Spirits are Spirits that can be evolved into newer Spirits after maxing out their level.
Enhanceable Spirits do not have a trait, instead stating that they can be enhanced once they reach Lv.99. Upon reaching Lv.99, the Spirit can then be enhanced into a stronger higher class Spirit who now grants a skill, generally being one that isn't found as a trait on a regular Primary Spirit. The Spirit's level resets to Lv.1 upon enhancing.
Enhanced Spirits are also numbered directly after their Enhanceable counterpart, and share the same Type and number of Slots as them.
List of Enhanceable Spirits
Enhanceable Spirits' abilities are not listed as they all say "Can be enhanced at Lv. 99".