Human Spirit of Steel
The Human Spirit of Steel was created from Ancient Wisemon after his battle with Lucemon in the past. From there it passed to Cherubimon's keeping. When Cherubimon betrayed the Digital World he transformed it into Mercuremon. Mercuremon is defeated by Takuya in "Takuya's Fusion Evolution, Aldamon's Explosive Attack" and the spirit is trapped inside his D-Scanner until he gives it to Kouji in "Spirits Become One! Takuya and Kouji's Ultimate Evolution!" to allow him to hyper spirit evolve into Magna Garurumon.
(Note: Is called Spirit of Steel H in the TCG.)