Rui Tachibana

Rui Tachibana (橘 瑠衣 Tachibana Rui) is one of the main protagonists of Domestic na Kanojo. She is the stepsister of Natsuo Fujii and the younger sister of Hina Tachibana. She is also pregnant with Natsuo's child.

Appearance
Rui is a girl with short blue hair and bright magenta eyes. During her time in high school, she is usually seen wearing her uniform, which consists of the standard white collar shirt, sweater vest, and a plaid skirt. After graduating high school, she dons casual clothing or a chef’s uniform for work. Rui occasionally wears pretty clothes on her monthly dates with Natsuo.

Personality
Rui is introduced as a cold and blank girl unwilling to talk to other people. At a mixer, she willingly asked Natsuo to skip out of the mixer out of boredom, with another pretence to have sex simply to understand how it felt.

Rui develops into a very kind and loving girl throughout the manga. Initially acting cold towards her step-brother, she gradually warms up to Natsuo, later developing feelings for him.

Natsuo Fujii
Rui's step-sibling after their parents arranged a remarriage. Though both already knew each other after their one night stand, Rui personally wanted him to forget what happened. However, after extensive thought of how she felt about Natsuo, she acknowledged that she was in love with him.

Their subsequent relationship does well until Rui decides to be a chef after meeting her biological father. During the progress on her career to be a chef, she took his invitation to learn more in America for a year. At the same time, Natsuo had developed writer's block and didn't tell Rui, depending on other girls whom she didn't know. Feeling bad for being unable to help and figuring both of them were burdening each other, Rui decided to break up after much thought, turning their relationship back to brother and sister.

Hina Tachibana
Rui and Hina share a close bond as sisters. Since elementary school, whenever Rui was feeling down, Hina would sneak into her bed to sleep together. when Hina noticed Rui was depressed, she would sneak into Rui's bed to sleep together. Rui admires and envies Hina's bright and sociable personality, which was why she wanted her to end her affair with Shu Hagiwara.

Momo Kawashibara
Momo is Rui's high school best friend and fellow former club mate. The first encounter is a pleasant one but filled with contradictions due to Momo's influence at school as a "whore." Rui didn't acknowledge the rumours.

Miu Ashihara
Miu is Rui's fellow clubmate and fellow second year. Rui first thought of her as a rival towards Natsuo, but Miu turned out to have a one-sided love for their club advisor and teacher, Reiji Kiriya.