Similar to other regions, Fontaine also has a city reputation system. By increasing your reputation level, you can earn achievements, certain items, discounts from merchants, and blueprints. Here's how to unlock the Fontaine Reputation:

Unlocking Fontaine Reputation: Completing the Quest

To unlock the reputation, you need to complete a small introductory quest called "Interview with a Steam Connoisseur." It will automatically appear in your available quests once you meet the conditions (which are: Adventure Rank 40 and completion of Chapter 4, Book 2 of the Archon Quests "We Will Be Reunited").

Chat with Euphrasie for a little bit - the NPC will be marked with a quest marker as usual. After the dialogue, the desired menu will pop up.

Done! Now, to increase your reputation level, you just need to regularly participate in activities, complete weekly requests, and explore the world.

Screenshots taken from KyoStinV's video.