Arata has short, slightly spiked dark brown hair, with the lower back portion shaved. He is the tallest among the Shiunji siblings and has a well-built physique from regular training. His narrow eyes and thick, downward-slanting eyebrows give him a stern, intense expression.

She wears her school uniform with a large butterfly-shaped tie and often carries a sports bag, reflecting her athletic nature. At home, she usually opts for simple, comfortable pajamas.

Arata is very protective of his family and caring toward his siblings, partly because he feels the weight of being the eldest male son and the heir to the Shiunji fortune. Despite his sharp and almost aggressive looking facial features, he becomes flustered very easily. He is shown to carefully think through his words and actions, although his intentions are often misunderstood. He usually turns to his brother Shion for advice, even though Shion is younger. Whenever one of his sisters approaches him in a sexual or romantic manner, whether jokingly or seriously, he quickly rejects them and reminds everyone that they are siblings regardless of blood relation.

Aside from the complicated situation within his family, he is also dealing with one sided feelings for Rara Yakoyama, the girl he has a crush on, who already has a boyfriend. He was too scared to make a move before, and now he has no idea if approaching her is still a good idea. It is unclear if Rara even knows he exists, as he always hides when he sees her and is too nervous to send her a friend request. While his personality and actions show other potential interests, such as spending time with his family, seeking guidance from his brother, or navigating his struggles with romance, the only activity explicitly highlighted is his dedication to working out.

The plot of The Shiunji Family Children centers on Arata Shiunji, the eldest son of a wealthy household, who learns that he and his six siblings are not related by blood. This revelation from their father completely alters their lives, especially Arata’s, as he struggles to process the truth and the complicated emotions that begin to surface within the family. The story delves into themes of belonging, identity, and the delicate balance between familial bonds and romantic tension, made even more complex by the fact that the siblings share no biological connection.