Dysfunctional (Fate/Youjo Senki/Worm crossover)

Counter Guardian EMIYA and Tanya von Degurechaff, reincarnated as siblings in the chaotic world of Worm, find themselves entangled in a web of power struggles, survival, and moral ambiguity. Neither knows the truth about the other, but both carry the scars of their former selves. As they navigate the deadly politics of the world around them, will they end up better or worse than before?