Weapon

Uncommon

Any weapon.

When your attack roll is one point away from landing a critical hit, once per long rests, you can choose to critically strike the target instead.
When you do so, the weapon corrects its own trajectory to guarantee a critical strike.

This can happen a lot of ways, some examples.
A soul fragment of an ancient master has been attached to the weapon, remembering its way to strike true and never miss its target.
Runes are carved into the weapon, when activated the runesslightly alter the weapons trajectory.
A sentient weapon, helping its user.