This is for the asker who sent in the Zankyou no Terror message!
There is an incredible ZnT crossover fic featuring Kageyama as Nine and Yamaguchi as Twelve because, in a not-at-all creepy coincidence, their voice actors play those characters respectively, and those are also their respective jersey numbers. Here it is:
Resonance by RubySmiley
Remember that we lived.”
Nine and Twelve’s distant legacies are remembered—by the two boys who live on in their names.