This popped up in my feed just as I was trying to organize my Genshin bookmarks, so let me just dump my reading history thoughts. Zhongli and Aether stories often build on that mentor-student, ancient-and-eternal-meets-young-and-mortal dynamic. You get a lot of fics exploring themes of legacy and memory—Zhongli carrying thousands of years of history and loss, Aether moving through worlds but always being the outsider. The angst potential is massive, obviously. A recurring thread I see is Zhongli teaching Aether about Liyue's past, but Aether inadvertently showing Zhongli how to live in the present, to find something new to care about after all his contracts are done. There's a quiet melancholy to it that a lot of writers capture really well, not just sad, but this gentle mourning for things that are gone paired with hope for what's being built. I've also noticed a sub-category of fics that flip the script, where Aether's own long lifespan and accumulated trauma from traveling gets centered, and Zhongli becomes the anchor, the steady rock in the storm. It's less common but really fascinating when done right. The emotional payoff usually hinges on that moment of mutual understanding, where the layers of formality and politeness finally peel back.
Another big one is the theme of service and devotion, but with a twist. It's not just Aether serving the Archon; it's often Zhongli, retired and mortal-coded, choosing to serve and protect Aether's journey. There's a bittersweetness there because they both know it's temporary—Aether will move on. That impermanence fuels so many slow-burn pining fics. Also, can't ignore the sheer number of coffee shop AUs or domestic fluff pieces that use them to explore themes of mundane happiness and simple companionship as a form of healing. After everything Zhongli's been through, just having a quiet place to belong seems to be the ultimate emotional goal for a lot of authors.