Final answer:
Gordon Allport would describe Yumiko's being shy as an introverted personality trait.
Step-by-step explanation:
Gordon Allport would probably describe Yumiko's being shy as an introverted personality trait. According to Allport's theory, introverts tend to have a higher need to be alone, engage in solitary behaviors, and limit their interactions with others. Being shy is often associated with introverted characteristics, such as feeling more comfortable in quieter settings and being more reserved in social situations.