Myrmidon (Fire Emblem class)

This subclass is largely inspired by the Fire Emblem games, referring to a very recurring class throughout the franchise, the myrmidon and master swordsman. Their resources are direct adaptations of active and passive skills they had in several games. Even having a simulation of the class promotion mechanic when reaching level 10, which in Fire Emblem games is the minimum level to promote. To use all the features of this subclass you must have a sword, any time of sword, like a shortsword, longsword, scimitar, rapier, greatsword etc...

Adept

Beginning when you choose this archetype at 3rd level, you can slash your enemies with Flashing Speed, after using an attack action wielding any type of sword on your turn, you can roll one d10, if you scroll a 9 or 10, you can do one extra weapon attack with your sword. You can only use this feature once per round, and twice per round when reach level 8
In addition, if you are wearing no armor, your AC = 10 + your Proficiency bonus + your Dexterity modifier. With this you can wear the stylish swordsman clothes found in the Fire Emblem games

Sword Vantage

Starting at 7th level, you can intercept enemy attacks with precise cuts. If a creature within 5 feet of you announces an attack against you, you can use your reaction and make an attack with your sword before it, hitting or missing, the creature then makes its attack normally.

Swordmaster

At 10th level, you promote your techniques by becoming a master in the use of the sword. Every time you make an attack using a sword you can score a critical hit on a roll of 19 or 20. That bonus on critical hit can Stack with other class, weapon or magic item features (Example: If you use the Hexblade curse together with this feature you can score a critical of 18 to 20 on the dice).

Swordfaire

Starting at 15th Level, you can apply your proficiency bonus to your damage rolls with sword attacks. And your sword attacks are considered magical for the purpose of overcoming resistances to non-magical attacks.

Hostile creatures have disadvantage when trying to disarm you, and if you are subject to a saving throw to avoid being disarmed while wielding your sword, you make the saving throw with advantage.

Astra

At 18th level, you learn the supreme swordsman technique, a starstrike capable of cutting everything and everyone with incredible speed. Whenever you use your action to make an attack using your sword, you must announce that you are using this ability in place of one of your normal attacks. And then you start a sequence of 5 consecutive attacks, on a hit this attack only deals half the damage (rounded up)
(Practical use: let's say you are able to make 3 attacks per turn, then you for example can make 2 regular attacks and replace the 3rd with the Astra, doing 5 more attacks with half damage, to a total of 7 sword slashs) 
You can use this ability a number of times equal to your proficiency modifier, but just once per turn. You regain all uses after you finish a short or long rest