Iron Core of Koa'ki Meiru

Iron Core of Koa'ki Meiru was introduced to the Yu-Gi-Oh! Trading Card Game as part of the Raging Battle set, with this specific ultra-rare version appearing in the 2009 Duelist Pack Collection Tin. The card serves as the central engine for the Koa'ki Meiru archetype, a group of rock, machine, and beast-warrior monsters designed around a maintenance cost mechanic that requires the player to discard this card or reveal a specific monster type during each end phase.

The card's design and mechanical concept were developed by Konami’s design team to encourage a high-stakes playstyle focused on resource management. Its artwork, featuring a glowing, unstable power source, reflects its role as the unstable catalyst keeping the robotic Koa'ki Meiru constructs operational. Upon release, it became a staple of competitive decks that could facilitate the archetype's aggressive board presence, earning it a reputation as a fundamental piece of card synergy in the late 2000s meta.