That's not what it looks like when a cat is done with it.
The way "Assassinating" is described as a fighting style makes no sense. It rrequires so high speed relative to your opponent that you don't have to use the style, and can just attack however. If you can move so fast you can create and attack a blind spot, you can just attack normally around the guard.
That breastplate wouldn't even cove the breasts of someone who has them. It should go down to your waist (your natural waist, not the waist according to modern pants), since that's where It otherwise starts to restrict your movement.
Real ninjas weren't assassins except by exception. They were more concerned with spying. If they had formal martial arts training, it would be normal samurai training, since many were samurai.
Shin guards aren't exactly vital protective equipment unless there's some magical reason for them. Those are also bracers, not leather gloves.
Slings are a bit hard to aim with, but if you're skilled they're severely underrated in almost all fiction. A typical sling would have a loop and a knot, not too loops, but it probably still works. But not like she's depicted using it.
The back of the shield looks weird. Like a centre-gripped shield but not at the centre, or one strap of a strapped shield.
Do Japanese say corn, or maize like the rest of the world? "Corn" was originally any grain, and is usually the name used for the local main cereal grain. In Sweden, we use "korn" to refer to barley, and we still have the meaning of "grain" (like "a grain of salt" would use "korn" for "grain").
That's a flock of wolves. Realistically, if that number attacked them, they'd be dead.
what is with this artist and armour?
Yeah, it's spotty at best. It's like sometimes they hit the right image source, but usually not. Weapons are usually better, but still a toss-up.