Expert Affinity is the key to building a good relationship with Experts. You can unlock an Expert when you have gained enough Expert Affinity.

There are 100 Affinity Levels, divided into 11 phases, ranging from Stranger to Intimate. By advancing the Affinity Level Phase with an Expert, you can enhance their Talent Skills.

You can gain Affinity with Experts by going on Treks with them or sending them gifts such as Compass, Fiery Heart, and Sail of Conquest.