You have to speak with Kayelinth on the beach at least once and then re-enter the map to make Jaylin appear.
Yes, there are currently only 4 "real" battles and the bonus battle that you can repeat endlessly for resources.
I plan to improve the system and add battles later, but due to the complexity it's very time consuming and nothing I can do just in between updates, so it's on hold until I get the more important stuff done.