Alright, let's talk about bottom Kaeya because wow, does the fandom have a type. A huge chunk of it revolves around Diluc/Kaeya, obviously. It's the classic angsty, childhood-friends-to-enemies-to-lovers drama, and Kaeya being on the bottom fits that dynamic of vulnerability and submission that the tension demands. Writers love exploring his guilt, the way he wears his secrets like armor, and then having Diluc be the one to break through it—physically and emotionally. It's all about that cathartic hurt/comfort, the ‘I hate you but I still care’ trope played out in every possible AU from canon-divergence to modern coffee shop settings.
Beyond the ever-present Kaeluc, there's a surprising amount of Kaeya/Albedo. The cold, analytical Albedo with the emotionally complex Kaeya creates this fascinating power dynamic where Kaeya’s usual flirtatious control gets dissected and reversed. It's less about raw angst and more about psychological unraveling, which is a fun shift. I've also seen a decent amount of him with Zhongli or even Childe, where the theme leans into Kaeya being outmatched by an ancient power or chaotic force, playing up his cunning against sheer, overwhelming strength.