Ronin

The Ronin is a Samurai with no master, specializing in single powerful strikes to defeat even the most powerful foes... with whatever weapon chosen, they become a master, focused in the art of honing that weapon till they become a legend with its use. This makes them less diverse, but highly focused and honed in the art of combat.

1.1: Fixed some text with the description to clarify something that was mentioned in the snippet but not the full description, may change more in 1.2 to add more balance to abilities.
1.2: Clarified Palm Strike ability and gave it its own damage value seperate from Iai-Jutsu Strike.
1.3: Updated Palm Strike to be more of a meme, which can be bypassed by healing magic or teleportation.

Iai-Jutsu Strike

When you choose this archetype at 3rd level, your weapon attack has advantage and +4d6 to damage to a strike against one opponent, either from stealth or combat once per short rest. At 7th this changes to 6d6, at 15th to 8d6.

Master of One

At 7th level, you can add double proficiency bonus (round up) to any weapon attack with a single chosen weapon. This weapon type is chosen at this level, and cannot be changed.

Death Chain

At 10th level, when an enemy is defeated in one strike, the Ronin may make another attack on an enemy within sight with advantage.

Five Star Palm Strike

At 15th level, the Ronin may make one unarmed strike against a living opponent who is bloodied as an attack action (half-health or less). When they are hit they take 10d6 damage for each square they travel by walking, flying, crawling, etc. until they die or are healed by magic. This attack does not get Advantage, and can only be done once per enemy per long rest. An enemy that teleports does not have to walk, and therefore is not effected by this until they do.

Lightning Samurai

At 18th level, the Ronin has advantage on all initiative checks.