Welcome! There are actually multiple ways to earn Feso.
1. Complete character recruitment quests, it will award you Sun/Moon/Growth Stones additionally.
2. Complete Scenario quests, some will award you Growth Stones. Example: Viron Scenario gives 100x Growth Stones
3. Increase your family level. As reward you get Family Level-up Gift Boxes. Some of those give you Growth Stones. Details can be found
here.
4. From completing Scenario quests you also receive "Pioneer Journals". These reward you certain items for each day you login to the game.
Some of those rewards are Growth Stones as well, details can be found
here.
5. You can buy "Growth Stones" from the Token Rank Merchant in almost every town.
6. You can do missions, roulette can award you Moon/Growth Stones. Your best chances are Bounty Hunt and Castilla missions.
If they are too hard, join some friends or clan members that do missions on daily basis. Hint: Bounty Hunt Bosses also drop Feso Stones, the roulette is just reward on top.
7. Finish Achievements for Infinito Challenge Rank 10 and 20, you will get 50x Growth Stones in total.
Have fun!