Mikadzuki no Hansha (Patreon)

Weapon (longsword), legendary (requires attunement)

This magical katana has the finesse property. It has 6 charges, and regains 1d6 charges daily after being bathed in moonlight for at least one hour. The blade loses all abilities on a moonless night.

When a creature makes a spell attack roll against you, you may use your reaction to hold out the empty sheath and cast Counterspell at a level equal to 3 + the number of charges you choose to expend (minimum 1). On a success, the spell is absorbed into the sheath. You can dip the blade into the energy within, coating the blade in magical energy for one hour. The blade deals additional radiant damage equal to the level of the absorbed spell. If multiple spells are absorbed this way, the additional damage is equal to the combined levels of those spells. If you make an attack while the additional damage is 10 or higher, roll 1d12. If you roll a 1, the blade shatters and must be reforged.

Crescent Moon Reflection. While spells are absorbed into the sheath, you may dip the sword into the magical energy within and slash outward, sending a crescent of magical energy screaming from the blade. The absorbed spells’ magic is expended and each creature within a 60-foot cone in front of you must make a DC 16 dexterity saving throw. On a failure they take 1d8 radiant damage for each level of spell released this way or half as much damage on a success.

The sword of a nameless warrior whose power was derived from the light of the moon. Though they themselves had no magical prowess, they had a weapon forged that could harness the magical energy of their enemies; a sheath, enchanted with the power to absorb spells thrown at them, and a sword that could be empowered with the absorbed spell. The warrior developed an ultimate attack, unleashing all of the stored energy within the blade outward in a crescent, resembling the reflection of the moon in still waters.