The echo
Each character carries an echo of itself. The primary form repeats at an offset and breaks down into fragments as it trails off, so the letterform is followed by a decaying version of its own geometry. The name comes from the behavior: the shape persists after the stroke ends.
The constraint
The constraint was building a full uppercase set where the grid handles every letter without exception. Letters like O, Q, and S have to resolve as facets rather than curves, and the echo has to remain legible as a repeat of that specific letter rather than generic texture.