The Way of the Kensei monk gets the One with the Blade feature at 6th level (Xanathar's Guide to Everything, p. 34-35):
At 6th level, you extend your ki into your kensei weapons, granting you the following benefits.
Magic Kensei Weapons. Your attacks with your kensei weapons count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage.
Deft Strike. When you hit a target with a kensei weapon, you can spend 1 ki point to cause the weapon to deal extra damage to the target equal to your Martial Arts die. You can use this feature only once on each of your turns.
So at level 6 a monk would use a ki point to add 1d6 dmg? This is instead of a Stunning Strike or Flurry of Blows? Is the damage bonus continuous through the turn with further weapon strikes?