The Abyss has been antagonized the cast of Genshin Impact since the start of the Traveler’s journey. Abyss mages have long been an enemy, as have Abyss Lectors. Unlike other mobs, though, the Abyss is being given a lot of development and seems to be the actual antagonist of the game.
The first major Abyss-related event was shown when Diluc took on some Abyss Mages outside of Mondstadt, and Dvalin was corrupted. From then onwards, the Fatui took over the antagonist role until you meet Dainslief in “Bough Keeper: Dainsleif” and in the events of “We Will be Reunited.”
Related: Is Paimon evil, the final boss, or just a friendly companion in Genshin Impact?
These two quests eventually lead players to learn that their lost twin is the prince/princess of the Abyss and the one pulling the strings behind the organization. You also learn that Abyss creatures were once the people of the fallen nation of Khaenri’ah.
The Abyss is revealed to be looking for a way to take down Celestia is as further proven by Enjou in Enkanomiya. To complicate matters further, Enjou even communicates to the Traveler that he likes them and even gives them a vague warning about trusting Paimon.
It’s also implied by your twin in “We Will be Reunited” that they want you to continue your journey so that you grasp what’s truly going on in Teyvat. This seems to point to the fact that your twin expects you to eventually assist them in their goal of taking on Celestia.
The Abyss isn’t good by any means, but it seems that all factions in Genshin Impact have their own goals. You are advised not to trust the archons by Dainslief, and the Fatui seem to be driven by the belief that the Tsaritsa will create a better world.
For more Genshin Impact content, check out How to unlock and complete the Answer Me This, Outlander recurring World Quest in Genshin Impact on Pro Game Guides.