ichidan verb / intransitive verb:

• to break (into pieces); to be broken; to be smashed
• to collapse; to crumble; to decline; to cool (e.g. enthusiasm); to dampen (e.g. one's will to fight)
• to become less formal; to throw off reserve; to become affable ➜ くだけた
• to become easy to understand (e.g. a story) ➜ くだけた
• to be worried