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After being stripped of her noble status due to her family’s downfall, the former aristocrat heroine is cruelly dumped by her fiancé, who cancels their engagement. She goes from riches to rags, forced to live as a commoner, learning to cook, clean, and work for the first time. The keyword specifies as the source
貴族から庶民になったので、婚約を解消されました！ - カドコミ forced to live as a commoner
If you are determined to find this raw chapter, follow these steps carefully: learning to cook