Sir Nighteye carried no offensive Quirk, so he carried these instead: little stamp-shaped slugs weighing five kilograms apiece. Thrown fast enough, one of them hits like artillery and gives him a reach his own body never provided.
Sir Nighteye kept a supply of these weapons on hand. Each one is small and shaped like a stamp, and each carries five kilograms of mass packed into that frame.
The seals become dangerous through sheer velocity. Hurled at extreme speed, they let their user open fire from a distance, which covers the gap left by a Quirk that offers nothing in a fight.
The force behind one is not modest. A single throw from Sir Nighteye wiped out one of Twice's Doubles outright.

Naruto vs Luffy with the twist nobody asked for: Luffy tickled Hinata on date night, and she kind of liked it. We break down the whole fight and commit to a winner....

There are no women on Namek. That isn't an oversight, it's the biology. Why we handed Piccolo the one thing his own species rules out, and why it had to be trap soul....
Sir Nighteye is the Pro Hero who carries the Hyper-Density Seals, small stamp-shaped weapons he throws at high velocity to compensate for a Quirk that offers nothing in a fight.
Each Hyper-Density Seal that Sir Nighteye carries weighs five kilograms, packed into a frame small enough to be shaped like a stamp.
The Hyper-Density Seals are small, stamp-shaped weapons carried by Sir Nighteye, each packing five kilograms of mass despite their compact size.
A single throw of a Hyper-Density Seal from Sir Nighteye was enough to wipe out one of Twice's Doubles outright, showing the force behind them at extreme velocity.
The Hyper-Density Seals come from an unidentified support company; My Hero Academia does not name their maker.
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