Fa Jin

Fa Jin, read in Japanese as Hakkei and glossed as "Force Discharge", was a Meta Ability that originated with Bruce Lee, passed afterward to Izuku Midoriya, and ended up in the possession of Tomura Shigaraki. It is a close-range Emitter power, debuting in Chapter 313 and Episode 134, and it ranks among the oldest Quirks the series knows of, a short list that also holds Life Force, Gearshift, Spearlike Bones, the unnamed Luminescence, plus One For All and its counterpart All For One.

The name is borrowed from an actual training concept in Chinese martial arts, foundational to styles including Jeet Kune Do, Bajiquan, and Taijiquan, where explosive movement and stomps produce devastating single strikes. Kohei Horikoshi described the underlying idea as aligning the body so that it releases explosive force through the smallest possible motion, and he wavered between this name and Charge-Up before settling.

Repetitive movement charges the power. Kinetic energy accumulates, glowing red as it gathers, and waits until the holder decides to spend it. Release delivers a violent jump in both speed and strength, usable through any part of the body, and the reserve can be drawn down in portions rather than all at once, which permits several separate bursts from a single charge.

Other Quirks accept the boost as well, which widens what the user can do with them. Blackwhip gains enough force to snare formidable opponents, and Float pairs with it for faster flight and easier steering. Stacked on top of the energy already banked inside One For All, the effect is dramatic: 45% of One For All, charged this way and slung with Blackwhip, reaches something comparable to full power, and does it without the backlash the body normally suffers.

Little is documented about the limits. What is suggested is that the charging phase takes a long time, and that spending the energy before it has properly built leaves the output well short of what it should have been.

Izuku Midoriya first reaches for it against Lady Nagant. Smokescreen obscures her sight while he vaults between buildings to charge, then leaps from a skyscraper to seize her; a further charge, showing how well the Quirk pairs with One For All, carries him past the speed of a bullet to pull Kai Chisaki clear, and Faux 100 Percent: Manchester Smash finally ends the fight.

Later pairings show the range of it. With Float and his Air Force technique he crossed an ocean. With Blackwhip against "Tomura Shigaraki" he formed Blackchain to bind him. With Gearshift he produced Overdrive, a surge the story puts at 120 percent of One For All's output. He also drove a massive Delaware Smash into the ground to interrupt Tomura's Decay, and rocketed himself upward for a kick that the villain slipped without effort.

The Quirk's end came when Izuku forced Fa Jin, along with most of the others he carried, into Tomura through blood in an attempt to break the villain's leaden soul. The transfer destroyed it. Named techniques built on it are Faux 100 Percent, Faux 100 Percent: Manchester Smash, Blackchain, and Overdrive.