While attuned, the arm replaces one missing arm or can sheath a willing creature's existing arm in hardlight. It functions as a normal arm and hand, and its bearer is proficient with the sword it creates. The sword deals 1d8 radiant damage on a hit, or 1d10 radiant damage when wielded in two hands. It has the versatile property. The wielder gains a (+3) bonus to attack and damage rolls made with it. Adapt these bonuses to the host game's equivalent weapon rules.

The sword's attacks count as magical and ignore resistance to radiant damage. On a hit, the wielder can expend 1 charge to deal an additional 4d8 radiant damage.

When the wielder or a creature within 10 feet is hit by an attack, the wielder can use a reaction and expend 1 charge to reduce the damage by 4d8 + the wielder's proficiency bonus. The arm must be able to perceive the attack.

As an action, expend 3 charges to cast a teleportation effect, transporting the wielder and up to six willing creatures within 10 feet to a known destination on the same plane, up to 1 mile away. The destination must be a place the wielder has visited or can clearly see. If the host game has no teleportation rules, the GM determines whether the journey succeeds based on distance and magical interference.

Once per long rest, the wielder can spend 5 minutes tracing a sequence of stellar marks to open a doorway to a safe, unoccupied chamber in the archive. The doorway remains open for 10 minutes. The archive contains records and diagrams relevant to cosmic machinery, but its location and contents are controlled by the GM. The doorway cannot be used to bypass a barrier that specifically prevents planar travel.

As an action, the bearer can remove and command the arm to move up to 30 feet per turn for up to 10 minutes. It can manipulate objects, open unlocked doors, or make one sword attack using the bearer's attack bonus each turn. It has AC 20 and 30 hit points. If reduced to 0 hit points, it vanishes and reforms on the bearer's body after 1 hour.