Yuka Endo is the younger sister of Arato Endo, living with him and their father in Shin Koiwa. Her father works as an hIE researcher for the Societal Automation Experiment, focusing on Next Generation Total Environment Cities. Yuka exhibits a cheerful and optimistic personality, contrasting with her brother's introspective nature. She faces academic challenges and displays a degree of dependency on others. While sometimes perceived as self-centered or spoiled, particularly by her brother who reflects on allowing this trait, she possesses deep care for her family, especially Arato. Her fondness for meat is noted.

Shortly after Arato brings the hIE Lacia into their home, Yuka develops an immediate liking for her. Without Arato's knowledge or consent, she enters Lacia into an online modeling audition, demonstrating initiative but also a tendency to act independently on significant decisions affecting others. Experiencing dangerous events, including being rescued from perilous situations, prompts noticeable development in Yuka. Following these incidents, she consciously adopts a more understanding and appreciative perspective towards her brother, acknowledging his efforts to protect her. This leads her to deliberately moderate her previously self-centered behavior, signifying maturation in her character and relationship with Arato.

She maintains friendships with Olga Suguri, Kengo Suguri's younger sister, and Shiori Kaidai, Ryo Kaidai's younger sister, forming part of her social circle outside family interactions.