Ratatosk

Ratatoskr's Chain (チェンの鎖; Retetosukkuru no kusari) is the third zanpakutō of the Two Legendary Zanpakutō, and is the zanpakutō that would allow its sister blades, Vedrfolnir and Nidhogg, to combine their abilities and achieve a state of power unrivaled in written history. However, its existence remains highly unknown; the only way to recognize that such an item actually exists would be to utilize knowledge of shinigami lore.