A Gu worm floated above Fang Yuan.
Fang Yuan's primeval sea slowly fell as he activated this Gu.
This Gu was like a black bone, its two ends were round and smooth, with a thin body. It was emitting black rays of light while floating in the air.
The black light shone upon Fang Yuan's body, passed through his skin and flesh, and brought changes in his skeleton.
Fang Yuan had already used iron bone Gu, his skeleton was pitch black and was firm like iron. But under the effect of this Gu, his skeleton slowly became more firm.
This was essence iron bone Gu, a rank four Gu; one could get iron bone Gu by reverse-refining it.
Three days after handing over the ancient bronze skin Gu, Li Xian personally came to deliver this Gu to Fang Yuan.
Essence iron bone Gu could make Fang Yuan's skeleton even more firm and the effect was many times stronger than iron bone Gu. But at the same time, the process needed much more time.
