Iron Will is a two-handed sword in NieR and NieR: Automata. It is easily the heaviest weapon in the game once it is repaired, but has amazing strength. It is given to Nier and repaired by Gideon at the Junk Heap, as part of the storyline. Iron Will is broken when first acquired. The blade is completely snapped near the hilt, giving it next to no range or Attack Power. It is repaired up to Level Two as part of the storyline.
Iron Will is found in the Flooded City of NieR: Automata. From the access point, you head toward the broken bridge with a bus and follow it down and on the right, there is a lip where Iron Will, can be found using the scanner to reveal the weapon.
NieR - "An enormous sword that grows heavier with every kill as blood and flesh cling to the blade."
We give the cry of life. Hot iron forms our body. Steel hammers temper our shape. The dim light of the forge and sparks of steel watch over us. We are the iron will. Born of the thundering roar.
We give the finality of death. Iron skin draws out fear and terror, and is bathed in flesh. We are satisfied by the snatching of life. We realize our purpose through the crushing of the bodies. In our delight, we spread death far and wide. We are the iron will. We kill. Kill. Kill. Kill.
We smash. Hate and anger tear our body up in the midst of blood and battle. Madness-inducing power raises a storm of blood and shrapnel. We battle the red dragon day, after day, after day. We are the iron will. Cursed steel sinks into the darkness of sleep.
We dream. The dream of a tiny butterfly, Wildly dancing in the rain. We are the iron will. We dream, a deep, unfulfilled dream.