The Serafim was a holy creature, blessed with divine power, a power that only belonged to her. She was the embodiment of pureness and compassion, someone without any sense of hatred, or anger.
But at the same time, she had a human heart, which brought about the contradiction to the purpose of her existence, and Na struggled to keep her heart pure after she met Lu.
That cursed creature was so… lively.
The way the lycan got angry on her behalf and felt upset, showing his emotions freely, which was something that a Serafim couldn't do, was a comforting thing for Na in a twisted way. She lived through Lu emotionally, until she grew attached to him, so did the lycan.
Thus, when she lost him, there was nothing that mattered in her eyes anymore. The pain was so great, she couldn't endure it.