It seems you are looking for a story inspired by of the English dub of Shinobi no Ittoki . In this episode, titled "Cycle of Fate," the tension between the Iga and Koga clans reaches a boiling point during the Ninja Academy exams.
In a desperate maneuver, Ittoki used his suit’s exhaust to create a smoke screen, not to escape, but to close the distance. He didn't strike with a blade. Instead, he used a palm strike to the chest, a move his mother had taught him—not to kill, but to disarm. Shinobi no Ittoki (Dub) Episode 5
As if on cue, a flurry of shuriken whistled through the air. Ittoki reacted by instinct, his Iga-built suit whirring to life, enhancing his speed just enough to deflect the steel. Out of the darkness stepped Haruka, a Koga student whose eyes held a fanatical gleam. It seems you are looking for a story
"The Iga heir," Haruka sneered, spinning a kunai between his fingers. "A boy playing dress-up. Do you think that suit makes you a ninja? You’re just a relic of a dying clan." He didn't strike with a blade
"I'm not going to kill you," Ittoki said, his voice steady for the first time. "Because if I do, someone else will come for me. And then someone will come for them. I’m done being a spoke in your wheel."
Kousetsu watched from the trees, a flicker of something—perhaps hope—crossing her features. The cycle hadn't broken yet, but for one night, in the heart of a simulated forest, the wheel had stopped turning.
The air in the Koga training grounds was thick with the scent of ozone and damp earth. Ittoki Sakuraba stood at the edge of the simulated forest, his lungs burning. He wasn't just fighting his classmates anymore; he was fighting the shadow of a father he never truly knew and a future he never asked for.