So you know how back before Twi became a princess, how even when they should've fought super dangerous threats, like Nightmare Moon n' Discord n' Chrysalis, the 'threats' were kind of...lackluster?
And even when it did get super dangerous, it was only during an invasion with Chrysalis, after having to deal with two pretty dang godly threats?

So like, I had a headcanon in which Celestia was using huge amounts of magic to mitigate and influence things within her domain to a certain degree, so that even meeting major threats would only cause 'lessons' for the new Elements of Harmony, and she's been doing that for years and years.

However, she's waning on power after a bunch of years of trying to do Luna's job, her job, and keeping up her influence in her land, so when Chrysalis came around, she was low on energy. So, to defend against more major threats, even during her tenures of power, she 'hired' people with special abilities or trained them, or things like that.
To a degree, it was like a hidden "Suicide Squad".(edited)

So! Kouma's not from Equestria. He's from Neighpon, a mirror of Japan. Within Japan there are clans of various 'professions'. Just like real world ninja clans, culinary 'artisry clans' Yakuza, and things like that.

Kouma belongs to one of the remaining protectorates of Neighpon, the Ryu-Ou Ninja clan. It's named as such because, legend has it, that during the time of strife with what's known as "Demons" in the modern age, they, along with 11 other clans, were blessed by the dragons. His clan, in particular, was blessed by the Dragon King.

While it blessed them with the use of tremendous amounts of Ki, bodily fortitude, mental prowess, and spiritual prowess, it locked away their ability to use magic. While this isn't as much of an issue for Pegasi or Earthen Pony...over 70% of the clan members are unicorns.
Now then, there are some issues with his family. As of late, since the elders are becoming more...liberal in attempt to get over the detriments their clan has, the old Clan leader, Kouma's dad, was allowed to marry outside of the country. As such, he married into a mystic clan of Zebra's. Similiar to Zecora's ilk.

That ain't what caused the trouble though. What caused the trouble is the bringing in of new ideas. Like travelling around a bunch. The clan heads and the future clan heads are not supposed to leave Neighpon under any circumstances.
His mom was a varied, storied traveller, which is how she met his dad. She caused a ruckus in one of the cities and his clan had to come and help out with it.

Well, The ruckus being an exorcism of an item from her homeland that had been smuggled into the country.
But that was years past. She told him of her travels since he excelled in all of his...studies, when it came to the clan. Especially in Ninpo usage, Ki Control, and Weapon use. To balance that out, she wanted him to have a more worldly view so he wouldn't be just used as a weapon.

As such, she implanted a wanderlust in him. When he wanted to 'study abroad' he was barred due to him being chosen to be next in line for leadership. So, he took one of the family swords, escaped his clan members, and escaped to Equestria.

However, he drew a bit too much attention since, even though he was well learned...all of his 'job' experience was through his Ninja missions(edited)
I mean. His knowledge of anatomy and grappling allowed him to be a self defense instructor and a Massage therapist.

But he didn't have the social faculties to really...function, y'know?
For the most part, he's adjusting. He's a quick learner, so he at least knows how to put on a facade that he's socially adept.
Partly because his civilian roommate keeps him in the loop of most things