This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / To Aruverse Rewrite Project
Chapter 8: When a crying Uiharu appears as her best friend just used Level Plus and gave herself progressive brain damage.
"Iíll see you again, okay? After I get outta here. We all will. And then we can do science again!" "Okay. Iíll...Iíll see you then. For Science!"
She never saw her students again.
Chapter 18: Ruiko wakes up after a cure for Level Plus' brain damage is found. The problem? They had to reverse the Kihara Process that made them Espers in the first place, resetting their levels back to Level 0. That means that all the progress and effort she spent after six years was for nothing, so when Misaka tries to cheer her up she takes it poorly.
When Accelerator leaves flowers for the dead children. It turns out he was one of Kiyama's students and likely had known at least some of them personally.
Kiyama's mind is so damaged that she'll never recover.
And now, as she lies in her hospital bed, bereft of muscle control, of memory, of sight and smell and taste, and yet somehow bereft of the mercy of unconsciousness as well, they watch her still. They watch as her mouth makes the same movements so many of her victims made, over and over again, though only the faintest whisper of breath accompanies them.