Quick answer: Heel Reinforcement Part is the reward for the side tale Use It Against Them in the Crimson Forest: beat Jade Dancer and Iron Fiend using only Fiend Saws and Iron Gauntlets.
Where to get Heel Reinforcement Part
Before you start, make sure you have the Fiend Saws and the Iron Gauntlets. Those two are the only weapons the fight allows.
Completing the tale under that weapon condition gives you Heel Reinforcement Part.
Heel Reinforcement Part item card
The item card reads:
It began when Xiaokui noticed the wear on Jade Dancer’s heels and gave her parts to reinforce them. As those parts wore out with use, Jade Dancer kept them instead of throwing them away.
The habit of using such fittings, however, has quietly stayed with her ever since.
Its effect line reads: “Used to Soul Temper the Fiend Saws.”
What Heel Reinforcement Part does
Heel Reinforcement Part is a Soul Tempering material for the Fiend Saws and nothing else. It sits alongside the other Soul Tempering materials, each tied to its own weapon.
In Pangzhen, find Myst at the Order’s underground tavern. Using Soul Tempering on the Fiend Saws takes 5,000 Remnant Dust and the Heel Reinforcement Part.
| Weapon | Upgrade | Cost |
|---|---|---|
 Fiend Saws | Endless Fiend Form | 5,000 Remnant Dust + Heel Reinforcement Part |
The upgrade is Endless Fiend Form, and its effect reads: “After Fiend-Aura Erosion erupts on an enemy, all attacks against them become unblockable for 3 seconds.”
