A Kagi line extends in the current direction as long as price keeps going. When price reverses by more than a set reversal amount, the line turns and moves sideways then in the new direction. When the line breaks above the previous swing high it thickens, called a yang line; when it breaks below the previous swing low it thins, called a yin line.
The thickness change is the signal: thick means demand has taken control, thin means supply has. Because the chart ignores time, long consolidations collapse into a small amount of horizontal space.
Kagi is rare in modern platforms and there is little robust evidence that its signals beat simpler swing-based rules. Treat it as a clean visualisation of swing-high and swing-low structure rather than a system in itself.
Related: renko-chart, point-and-figure