Nunchaku are martial, blunt melee weapons consisting out of two batons connected to each other via a chain that deal 1d6 bludgeoning damage on a hit that have the Finesse, Special and Versatile properties.

Properties

Finesse
When making an attack with a Finesse weapon, you use your choice of your Strength or Dexterity modifier for the attack and damage rolls. You must use the same modifier for both rolls.

Special: Flourish
When you are wielding the nunchaku in two hands and take the Attack action on your turn, you can attempt to flourish with the weapon immediately before you make your first attack. To flourish, make a DC 13 Dexterity check, adding your proficiency bonus if you are proficient with nunchaku. On a success, you gain a +2 bonus to the first attack roll you make this turn. On a failure, you deal bludgeoning damage to yourself equal to your proficiency bonus and gain no bonus from your flourishes this turn

Versatile
This weapon can be used with one or two hands. This weapon deals 1d8 slashing damage on a hit if you are wielding it with both hands.

Superior Strike

Whirling Strike.
In a blitzing vortex of aggression, you strike at all those around you in a sinuous assault. Each creature within your reach must make a Dexterity saving throw. A creature takes damage of your weapon’s type equalling a number of d6s equal to your proficiency bonus on a failure, or half as much damage on a success. Success or failure, the creature can’t make opportunity attacks against you until the end of this turn.