I've been working at writing up a version of Kensei for 5e, and I'd appreciate your feedback. The concept is based loosely on the 3.5 Kensai, with some tweaks.
At 3rd level, a monk may choose to belong to the Kensei tradition. Kenseis are masters of the sword, and their god-like speed serves them well in combat. As a Kensei, you gain proficiency in the long sword and treat it as a monk weapon. In addition, you may wear light or medium armor and still use your monk abilities. You gain the following ability:
Iaijutsu: When your weapon is sheathed, you can react swiftly to an enemy attacking you. Before the enemy's attack is resolved, make an attack against that enemy with advantage.
At 6th level, you gain the ability Flash Step. Your blinding speed allows you to cover distances almost instantly. As a bonus action, you can teleport up to 60' to any space you can see. You then gain advantage to the next attack you make before the end of the turn.
At 11th level, you can make a Perfect Defense. Your superior speed gives you the ability to deflect all attacks. You may not take any action this turn other than a reaction, but all weapon attacks against you fail.
At 17th level, you learn the ultimate technique, Weaponsoul Dance. You may make three attacks with your sword against three different opponents no more than 30 feet from each other. Each attack is made with advantage and does double damage if it hits, as if it were a critical hit.
At 3rd level, a monk may choose to belong to the Kensei tradition. Kenseis are masters of the sword, and their god-like speed serves them well in combat. As a Kensei, you gain proficiency in the long sword and treat it as a monk weapon. In addition, you may wear light or medium armor and still use your monk abilities. You gain the following ability:
Iaijutsu: When your weapon is sheathed, you can react swiftly to an enemy attacking you. Before the enemy's attack is resolved, make an attack against that enemy with advantage.
At 6th level, you gain the ability Flash Step. Your blinding speed allows you to cover distances almost instantly. As a bonus action, you can teleport up to 60' to any space you can see. You then gain advantage to the next attack you make before the end of the turn.
At 11th level, you can make a Perfect Defense. Your superior speed gives you the ability to deflect all attacks. You may not take any action this turn other than a reaction, but all weapon attacks against you fail.
At 17th level, you learn the ultimate technique, Weaponsoul Dance. You may make three attacks with your sword against three different opponents no more than 30 feet from each other. Each attack is made with advantage and does double damage if it hits, as if it were a critical hit.