weep, grieve
忼 centers on deep emotional distress: weeping or grieving from sorrow or loss.
忼 combines the heart radical 忄 with 亢, which likely contributes the sound. The exact historical development is uncertain, but the structure suggests a phono-semantic compound related to emotional states.
The heart radical 忄 beside 亢 (which looks like a person with a heavy load) suggests a heart weighed down by sorrow, leading to weeping and grief.
For コウ, imagine a grieving person crying out 'Koh!' as they weep: Koh -> コウ, and the heart 忄 is heavy with grief.