Dusksong & Dawnsvoice
From D&D Wiki
Weapon, very rare (requires attunement)
These twin curved blades have glyphs carved into them that are mirrored on each blade. A dim light appears to glow from the glyphs.
If the scimitar' are moved more than 10 ft apart or if the glyphs on the swords are kept in total darkness for more than a day then the glyphs pulse red and stop glowing, any granted abilities cease to work.
Nimble: Whilst attuned to the blades, your movement speed increases by 10 feet.
Deadly: As you have become more attuned with the blades they grant you +2 to attack and damage rolls.
Perfect Offence: once per day when attacked you can spend your reaction after taking damage to perform a riposte manoeuvre counter-attacking and adding an extra 1d6 damage. (2d6 at lvl5, 3d6 lvl8, 4d6 lvl12)
Perfect Defence: once per day you can spend your reaction to block any melee based attack and sustain no damage, you may use this ability after the DM has rolled to hit but before damage taken is declared.
Note: The abilities are designed to be unlocked by the wielder. You probably do not grant them all at once.