Item from Sword Art Online by Reki Kawahara
A teardrop-shaped crystal containing a compressed AI consciousness — the item that saved Yui from deletion and lets her exist across any virtual world Kirito enters.
When the Cardinal System attempted to delete Yui as a rogue program, Kirito converted her core data into an in-game object — Yui's Heart — preserving her consciousness in a portable format. The item allows Yui to be 'revived' in any Seed-based virtual world by loading her data into the local system. It's the series' most emotionally loaded item: a father saving his daughter by turning her into jewelry. The fact that it works — that Yui can be restored from this crystal with her memories, personality, and love intact — is both a triumph of virtual technology and a reminder of how fragile artificial life is. She exists because someone thought to save her. She could cease to exist if the crystal is destroyed.
A small, translucent crystal in the shape of a teardrop, glowing faintly with warm light. It's the size of a pendant and is usually worn as a necklace by Asuna or carried by Kirito. Despite its tiny size, it contains the complete consciousness of an AI sophisticated enough to process the emotions of ten thousand people.
Also known as: Yui's Heart, MHCP001 Core