跡 means 'trace'

All four essays involve digging into matters, examining physical evidence of the past (including ruins, footprints, or even handwriting), making discoveries, drawing conclusions about what happened, and then taking action. That could mean closing the case on a crime, declaring a missing person legally dead and doling out inheritance money, reconstructing a historic site, or pursuing someone who has disappeared. All four essays reinforce the idea that although a living creature can vanish or die ridiculously fast, we all leave marks on this world.

Japanese calligraphy reflects the state of an artist's mind, spirit, and body. In one novel, a character studies her father's brushstrokes to assess his health. Applying ink to paper is soulful; one leaves behind traces of oneself that way. As essay 1821 shows, Zen has influenced sumi-e (ink paintings). That essay examines calligraphy and sumi-e from all angles, as do the other essays to some degree, including the way to liquefy inksticks (a meditative practice), the red marks with which teachers correct calligraphy, the vermilion stamps that serve as calligraphers' signatures, and the significance of bold strokes versus diluted ones.