Iron Bone Gu

It is like a bone, with rounded and smooth ends and a slender mid-area. The whole bone is jet-black as if made from iron. ^{ch. 232}

In the aperture it looks like a bone with rounded, smooth ends and a slender middle, jet-black as if made of iron. It is a rank three Gu that needs a large burst of primeval essence to activate. ^{ch. 232} A later summary repeats that the Iron Bone Gu Fang Yuan used was rank three. ^{ch. 345}

When activated, the Gu melts into iron liquid, leaves the aperture, and merges with the user’s skeleton. After the process finishes, the bones are dyed black, ^{ch. 232} and tough as iron. The change is a body remodel of the same family as other permanent bone and body Gu in that stretch: once done, Fang Yuan can stack Crocodile Strength Gu on top of his earlier boar strength because the skeleton can bear it. ^{ch. 233}

It is an expendable Gu. One successful use spends it. ^{ch. 288} The use is extremely painful. Losing consciousness mid-process wastes the attempt, and the text says many Gu Masters have died from that pain. ^{ch. 232} It groups with bronze skin Gu as a consumed Gu that leaves imprints on the body. ^{ch. 500}

While the Gu is still held before use, Bai Ning Bing scolds Fang Yuan for wasting spring milk nurturing it and Jade Bone Gu for days. ^{ch. 232} No cited chapter names any other food for Iron Bone Gu. One successful use spends the Gu, so the text never describes a long-term diet after activation. ^{ch. 288}

Still only rank one, he activates it with snow silver primeval essence transferred from Bai Ning Bing. He finishes the remodel without fainting, then spends the next day nearly unable to move while the pain lingers. Bai Ning Bing had urged him to use it sooner; while they delayed, they fed the Gu spring milk. ^{ch. 232} That transfer rests on Bone Flesh Unity Gu. ^{ch. 229 ch. 230 ch. 231}

No cited chapter assigns Iron Bone Gu to a named cultivation path that this wiki has a page for. It groups with Steel Tendon Gu and copper skin Gu as rank three body transform Gu Fang Yuan used. ^{ch. 345}

Later Fang Yuan uses Essence Iron Bone Gu, a rank four Gu from which Iron Bone Gu can be obtained by reverse refining. That Gu hardens the already iron-remodeled skeleton further, but the process takes much longer than the single-use Iron Bone Gu. ^{ch. 355}