You are a master swordsman.

Bonus Proficiencies

At 3rd level, you gain proficiency in Athletics and Perception.

Sword Strike

At 3rd level, you have mastered the art of swordsmanship. You learn how to break an opponent's stance, giving you the following benefits: 

• When you hit a creature with an attack, you can choose to force it to make a Strength saving throw. If it fails, it has disadvantage on all attacks it makes before the end of its next turn, and you have advantage on all attacks you make against it on your next turn. The DC for this save is 8 + your proficiency + your Strength or Dexterity modifier.

You can only use Sword Strike up to three times per short rest. You can only use Sword Strike once per round.

Unleashed Strike

At 7th level, when you land an attack on an opponent, you can choose to enhance said attack, granting the following benefits:

• Your weapon deals an extra 2d6 damage of your sword's type for this attack.
• Your AC is increased by 2 until the start of your next turn.
• This attack is considered magical for the purposes of overcoming resistance.

Once you have used this feature, you cannot use it again until you have finished a short rest.

Dueling Grounds

At 10th level, you can take an opponent with you into a duel to the death:

• You can transport yourself a hostile creature within 30 feet of you into an extradimensional space as a bonus action.
• This extradimensional space is a 30 foot diameter circle. You and the opponent brought in are placed on opposing ends of the circle.
• This lasts until one of the creatures in the space is brought to 0 hit points, or until you end it as a bonus action.
  
• After this feature ends, both you and your opponent are returned to the locations you were in before it was initiated.

Once you have used this feature, you cannot use it again until you finish a long rest.

Unleashed Blade

At 15th level, you have mastered your sword and can now wield it at full power for an extended period of time. As a bonus action, you can enter a stance that lasts until the end of combat, during which you gain the following benefits:

• Your AC is increased by 2.
• Your sword deals an extra 2d6 damage of its damage type.
• Your sword attacks are considered magical for the purposes of overcoming resistance.

After this stance ends, you cannot re-enter the stance until after finishing a long rest. You cannot use Unleashed Strike while in this stance. If you wield two swords, this only affects one of them.

Sword Expert

At 18th level, you have become so accustomed to the use of swords that your prowess with them is noticeably greater than your skill with other weapons. You deal half of your proficiency bonus as additional damage on damage rolls made with swords.

D&D Beyond does not support this, so simply add 3 to the damage modifier(s) of your sword(s) in the character sheet.