Plan
A cheap tree has a plan. A plan to stay cheap.
Picture a tree coming up with some elaborate plans to make sure they can spend as little money as possible.
あん
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The cheap tree's plan involves only buying anchovies (あん) and surviving on them. Good exposure to the sun and fresh water is too expensive. The tree plans to save money by eating anchovies.
You're not sure about this anchovy plan. Are you cheap enough to choose a life of eating only anchovies?