Every sword worthy of being called a divine weapon has a unique bonding pattern.

Furthermore, each covenant pattern is used only once before it automatically changes. No one but the sword itself knows it.

Before a sword spirit is born, the sword itself assesses whether the person wielding it is worthy of ownership, and only then is the pattern revealed.

But Immortal-Slayer, since its birth, had never acknowledged a master. The covenants it had formed were always with a companion spirit or a sword wielder.