shirou with nirvasyl syndrome is genuinely so terrifying like. obviously all the beastmen with nirvasyl syndrome are scary but shirou.. just the fact that it's SO different to how he usually behaves: shirou kills people and gets in a lot of fights but he doesn't relish in it, he doesn't enjoy it, he doesn't drag it out longer than it has to be or do anything that doesn't need to be done. shirou is obviously incredibly powerful and could do so much irreparable damage if he wanted to, but he doesn't!! shirou spends the whole show restraining himself because he knows he's dangerous, he knows he could hurt the people he cares about. he's smart and in control - he always bails michiru out of tricky situations, he always knows what to do to save the day. frankly, he's probably afraid of his true powers: in ep 12 he doesn't kill Alan because he doesn't want michiru to see that - and it's not bc he doesn't want her to watch him kill Alan (she's seen him kill multiple people) it's because he doesn't want her to watch him kill Alan like that by using his silver wolf powers. he doesn't want her to see what a monster he is on the inside, how dangerous and bloodthirsty he really is
which is why nirvasyl shirou is so much more gut wrenching than the other nirvasyl beastmen: shirou doesn't take part in needless violence, shirou isn't deranged, shirou isn't something to be afraid of, shirou isn't a bloodthirsty monster.
and here's michiru, facing the worst thing she's ever faced, and in any other situation shirou would be right there to protect her. but here, he's the thing she needs protected from
Owwwwww