Shouyou dies AU, where Shouyou does succeed in dying. This is Angst Central because he probably says something kind to Takasugi before taking his last breath that will haunt him to the rest of his days, plus Takasugi still has some of Shouyou’s blood in him (not sure if this has been covered by the anime, but basically when Takasugi was at death’s door he had a blood transfusion from Utsuro) and it’s been shown in the manga that just having his blood can lead to him having some control over you. Takasugi doesn’t have enough blood for Utsuro to do that, but my headcanon is that he can feel/hear Shouyou’s thoughts in his mind. so extra angst basically. 

Then there are the AUs where Shouyou never died in the first place, that the three of them successfully rescued him, but then he has to tell them the truth of his origins in order to explain why the Government and Oboro want him so much. So you have them all on the run, and the Joui3 struggling with this bombshell, and then Shouyou probably tries to go and give himself into the Government anyway, telling them that it’s all for the best because someone like him should die anyway. Cue Takasugi angrily telling him to cut that shit out and keeping him under surveillance 24/7, all while the war’s still raging on. 

I also like the idea of fics that aren’t necessarily AUs but that look back at their Shoka Sonjuku days where Takasugi just kind of admires Shouyou from afar and pines after him, or where Shouyou hints at his own past through cryptic words or actions. Bonus points for Takasugi himself remembering the past and putting those bits and pieces together. 

(Also Takasugi fighting Utsuro and being gutted by it, because it’s Sensei’s face but it’s not Sensei. Meanwhile Utsuro taunts him about his weakness) 

And then you have other classic Immortal AUs, like Shouyou being some mountain god and Takasugi being a boy he randomly meets or who’s sacrificed to him or who passes by his temple a lot. Or where Takasugi meets Shouyou at different points of his life and falling in love, but dealing with the classic dilemma of him aging while Shouyou isn’t. And then maybe Takasugi, in order to be with Shouyou or to match him in power, works really hard to develop his own magic or powers, but then goes too far into it and loses himself. OHHH and there’s the Cupid and Psyche myth AU, where Takasugi is wedded to a mysterious man who never shows himself and only comes to the bed at night and forbids him from seeing his face. 

(Spoiler)