The Shimamura clan have a special way of fighting derived from the clan's forefather, Yoshimotosana Shimamura, an olden and foreign traveler from lands unknown to Faerûn entirely. The Shimamura estate is rumored to be of origin from the far south-eastern part of the world, but no one apart from the actual Shimamura clan or any sort of family they harbor actually knows, and none of them ever have told of these lands. The fighting style of the Shimamura clan involves many various techniques involving stunning the opponent with the Shimamura's special Lightning Ki techniques.

Backstory Requirement: Shimamura Heritage

In order to possess this subclass, your character must, in some way, be tied to the Shimamura bloodline, either through marriage, blood, servitude or method, but residents from Faerûn would not know of this martial art at all. This rule can always be bypassed with your DM's permission, but typically it would make more sense to include an explanation in your description. The lore of the Shimamura clan can be entirely homebrewed to the DM's pleasure, or be deemed entirely unimportant as a whole.

Lightning Aura

When you choose this subclass at 3rd level, you gain resistance to Lightning damage. This is due to your Ki's natural lightning generation having trained your body to withstand it's influence on your muscles.

Denjiha

At 3rd level of this subclass, you can make a ranged Lightning spell attack as an action in combat for 1 Ki point. This attack does your martial arts die in Lightning damage in a straight line up to 30 ft in front of you. You cast this spell using your Dexterity modifier plus your proficiency bonus.

When you gain the Extra Attack feature, this special attack can be used for any of the attacks you make as part of the Attack action.

"... as Yoshimotosana rose from the previous attack made upon him, he loudly declared 'Denjiha!' as he sent a beam of lightning into his foe from his palm, ending the fight instantly." ~ Scripture on Yoshimotosana's first tournament bout.

Raijinken

At 6th level, at the cost of 2 Ki points as a bonus action, you may deliver a devastating blow reinforced with electricity to your target's midsection that deals your martial arts die in damage. That creature must succeed on a CON save (DC16) or become stunned till the start of your next turn.

Raiu Stance

At 11th level, you can enter a stance known as 'Raiu Stance' as a bonus action to either increase your walking speed or sacrifice it all in order to regenerate Ki Points.

You can expend up to 3 ki points to increase your movement speed until the end of the encounter. For each point you expend, your walking speed increases by 10ft.

Alternatively, you can sacrifice all of your walking speed for Ki Points instead. For each 15 ft of walking speed you sacrifice this turn, you gain 1 Ki Point in return. You must sacrifice all of your speed if you wish to use this feature. Your walking speed returns to normal at the start of your next turn.

"As all seemed to be over for Yoshimotosana, he gained a sudden burst of energy out of seemingly nowhere as he rose from the ground and onto his feet, delivering a final and fatal blow to Lord Goya's midsection, completely stopping his heart." ~ Scripture on Yoshimotosana's battle with Lord Goya.

Hissatsu No Raikōken

Ending at 17th level, for 3 ki points as an attack action, you can deliver a killing blow to your target by filling their body with black lightning ki, effectively stopping their bodily functions instantly upon failure of a CON save. If the creature succeeds the CON save however, they instead take 25d4 lightning damage. Creatures immune to lightning damage are instead resistant to this specific attack. This attack is made with your WIS modifier + proficiency bonus and counts as an unarmed strike.

"Yoshimotosana's magnum opus, Hissatsu No Raikōken, was only performed once in his lifetime, and it was near the end of his life. He ended his friend's suffering by performing this move upon them. This was the only recorded time that Yoshi shed tears publicly. A truly horrific sight indeed." ~ last words of Master Kentaro's Journal Entry #959 entitled 'The FInal Days of Yoshimotosana'.