setting sun
暼 centers on the sun setting, the moment when daylight fades and the sun disappears below the horizon.
暼 combines 敝 (worn out, tattered) with 日 (sun), suggesting the sun becoming worn out or fading as it sets. The exact historical development is uncertain.
The top part 敝 looks like something tattered or breaking apart, and the bottom 日 is the sun. Picture the sun breaking apart and fading away as it sets.
For ヘツ, imagine the sun setting with a heavy, tired sigh: 'hets' (like a breathy 'hetsu'). The sound of exhaustion cues ヘツ as the sun gives out.
—