stairs, flight of steps, degree, class, rank, step
堦 centers on a structured series of steps: a staircase, a flight of steps, or a metaphorical step in rank or degree.
堦 combines 土 (earth, ground) with 皆, which likely contributes the sound and the idea of a series or all together, suggesting earthen steps or a graded series.
The left side is earth 土, and the right side 皆 suggests a series or all together. Picture an earthen staircase where each step is made of packed soil, forming a complete flight.
For カイ, imagine climbing a flight of earthen steps and reaching the top with a satisfied 'Kai!' sound: Kai -> カイ, as you conquer the stairs.
—