Your expertise with the Twinblade allows you to turn your defensive flourish into an offensive strike. You gain the following benefits.
Ability Score Increase. Increase your Strength or Dexterity score by 1, to a maximum of 20.
Blade Graze. When you use the Whirl property, you can make one additional melee attack with the Twinblade. This attack uses the same ability modifier as the primary attack, and the weapon’s damage die for this attack is a d4.
Reactive Strike. When you use the Whirl property, until the start of your next turn other creatures provoke an Opportunity Attack from you when they enter your reach, or make a melee attack against you while within your reach.