Fenrick's left arm was completely severed, but all he could do was cover the gap with his right hand and try not to bleed to death.
Seeing his calmness, Shizune remembered a month ago when she had joined the training with the other knights because suddenly her physical abilities were growing at a much faster rate than before. Seeing that she was able to train more every day than the day before, Alphenzo regretfully said that it was a mistake for her to choose the path of magic. So Shizune trained for a while to improve her physical abilities as much as possible.
One of the most important things she learned during these trainings was that enduring pain is one of the most classic trainings of a knight.
When Shizune saw how much pain he could endure, she realized that the difference between them was not going to diminish just because she took his arm off.