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For the sake of her senior brother's happiness, she resolutely assumed her name, thinking that everything would be fine from now on. Who would have expected that everything about her would start to change as soon as he came back. She began to guard against him everywhere but couldn't control herself, and often showed her true nature. She thought he was teasing her because he found out her identity, which was true, but... He had known for a long time that she was not a little sister, but he didn't want to tell her early in order to see her angry expression from time to time. Until, trouble started to find her, and he had to be a troubleshooter...