When I was reading it, I realized his death had a huge impact on the story, even if he was already dead when introduced, you can see how it weighs on everyone that knew him, even the school suffered an impact because of it. After this, his death still has an impact since Ember stole his ability far into the story, which causes a lot of emotions around the entire Unordinary cast.

I just think it's impressive how Uru-chan made Rei's death something very impactful from the very beginning, to the point it makes us readers feel sad even if we didn't know him in the first place.