low-lying land, (kokuji)
圷 centers on low-lying land, specifically a type of marshy or damp ground. It is a kokuji created in Japan for this geographic concept.
圷 is a Japanese kokuji formed by combining 土 (earth, ground) with 下 (below, down) to express low-lying land. The exact historical origin is uncertain, but the component choice directly reflects the meaning.
The left side is earth 土 and the right side is below 下. Picture land that sits below the surrounding area, a low-lying damp field.
For あくつ, imagine a low-lying field where you need to act (あく) to drain the water, and you use two (つ) pumps. Act-two -> あくつ.
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red variety of Welsh onion grown in Ibaraki Prefecture