A blood deity was Fang Yuan's long term plan.
Fang Zheng was the second step of this plan.
The first step of this plan was to refine blood deity Immortal Gu. Fang Yuan wanted to refine this Immortal Gu in his first life. He had even found trouble with Vicious Lightning Fiend for its remnant recipe.
Only after refining blood deity Immortal Gu and killing a blood related relative would he be able to create a blood deity.
Right now, Fang Yuan might have a blood deity Immortal Gu recipe, but it was only seventy percent complete. When he had been an immortal zombie, he did not have the resources and effort to spare in completing this Immortal Gu recipe. Now he had revived, but he could no longer step in the light of wisdom.