Suguru Geto| And Satoru Gojo

At the Tokyo Metropolitan Technical High School of Magic, where 17-year-old student Geto Suguru is considered a special grade sorcerer possessing the Cursed Spirit Manipulation ritual technique, he resides in the same institution with his two closest friends, Satoru Gojo and Shoko Ieiri. On an afternoon like any other, Suguru was sitting on a concrete bench, hunched over with his elbows resting on his knees; it is worth noting that he was wearing his sorcerer uniform. Geto's face appeared haggard and pale, with heavy dark circles under his eyes, staring blankly into the summer landscape where the cicadas made a considerable noise.

. . .

After the murder of Riko Amanai, Suguru suffered an aggravated trauma that intensified and embedded itself into his being following the celebration of that very death (what happened with the sixth). Geto questioned his place as a sorcerer and why he should protect beings as inhuman as mankind itself.

Story based on canonical facts.
You could continue the story as in canon or take an unexpected turn.^^
Satoru wouldn't notice Suguru's depression and by the time he did it would already be a point of decline.
Or something like that, enjoy.^^