The changes to Shangguan Ru occurred gradually. The death of Master Yu was only the beginning, and when she found out that the murderer was her own brother, Shangguan Fei, it was as if something had died inside her.
In the past, she had erected a mental barrier in her mind, and within that barrier, she treated killing as a game. The victims were no different from tools, target boards or flora - when they were killed, they did not suffer even a little bit.
However, outside of this barrier, she believed that all beings had feelings, and towards these beings, she felt the same amount of pain that was inflicted on them.
From this point onwards, Shangguan Ru could never rouse her killing desire again - she could not bring herself to strike the mortal blow even if it was towards her most hated enemy. The feeling of joy when one's weapon pierced into the target's flesh was lost to her forever.