How about an idea for a monk? Always fun to learn new folklore!
Monk-Student of Ōya no Tarō Mitsukuni
Monks that follow Ōya no Tarō Mitsukuni follow this samurai due to his battle prowess and ability to overcome the impossible. Having heard tales of this man kill the unkillable giant skeletons sent against him by a practitioner of black magic, you now learn at the feat of the master as he reveals his secrets to you. He is a warrior first and an honorable competent second, but you find it hard to belittle the man for his results. You now learn to combine his techniques with your monastic training to survive the unsurvivable.
Path of the Sword
Starting when you choose this tradition at 3rd level, you learn how to use a longsword/katana. This weapon counts as a monk weapon for your flurry of blows. When you increase your unarmed damage, increase your longsword damage as well.
Learning From Your Foe
At 6th level you learn how the masters sneak into the enemy’s home and even their very bed to learn the secrets of its attack. You gain proficiency in Deception and Stealth skills. If you are already proficient in either of these skills, gain a +2 bonus to that skill instead.
Mastery of Onmyōdō
Beginning at 11th level, the master reveals the magics of life and death to you and how to survive the magic assaults on your life. When you are attacked by a magic attack or effect, you can spend a ki point to gain advantage on the saving throw.
Against the Impossible
At 17th level you no longer need the master to teach you how to do what must be done, you have learned to master the impossible. When you would be reduced to zero hit points, you can spend 3 or all your remaining ki points (whichever is less) to avoid the attack and gain hit points up to your maximum. You can only do this once and then you must complete a long rest before you can use this feature again.