In the Demon City, killing demon beasts can make one stronger, with a very small chance of obtaining an Illusory Object.
Wu Pifu had not yet obtained an Illusory Object, but he already understood what it meant to become stronger...
Negative!
To be precise, it was something akin to negativity.
When he killed the monsters within the Demon City, the weaker monsters did not show it clearly, but after killing slightly stronger and larger monsters, faint specks of light would appear in the pulverized remains, and these specks would enter his body.
As these specks of light entered him, his physical body began to change; his qi and blood surged as if he had consumed a miraculous elixir, running vigorously through his body, with great strength being born within.
However, at the same time, his Bu Mei Ling Guang was slightly suppressed, its radiance dimming, and faint negative emotions flickered in his mind.
Some form of pollution was stimulating his flesh and spirit.
Wu Pifu did not know how others felt, but having cultivated Bu Mei Ling Guang, he was particularly sensitive to this.
This peculiar foreign energy stimulated his physical body to continuously grow stronger, but it also increased his negative burden.