Shougo Mikadono (帝野 将悟/Mikadono Shōgo) is the protagonist of Kono Naka ni Hitori, Imouto ga Iru!.
Shougo is a handsome teenage with chin-length brown hair and gray/blue eyes. He is usually seen wearing the Miryuin Academy uniform.
Ever since he was a child, Shougo has been a kind and caring person who can easily make friends and attract girls because of that. Furthermore, Shougo possesses an eyes for details, and the ability to deduc the mysteries around him through observation.
Though Shougo at first did not wish to inherit the Mikadono Group, he nevertheless possessed a business acumen.
Because Shougo's mother Kanoko Mikadono was unable to get pregnant with her husband Kumagorou Mikadono, she conceived Shougo through artificial insemination with another man. Shougo grew up as Kumagorous's son and had no knowledge about his true father.
When he was a child, Shougo befriended Konoe Tsuruma and Miyabi Kannagi, the latter of which was saved by Shougo during a car accident. However, Shougo was injured in said incident, which created a scar on his forehead and caused him to lose parts of his memory, including his friendship with Konoe and Miyabi.
Following Kumagorou's death, in order for Shougo to inherit the Mikadono Group, he was required to graduate from high school, as well as finding a spouse. He enrolled in the Miryuin Academy because of that, and was coincidentally put into the same class as Konoe and Miyabi.
Things became complicated after Shougo learnt that he had a younger sister who attended Miryuin Academy and was constantly watching over him. Shougo was determined to find out about the true identity of this mysterious sister. He established the help of Ikusu Mizutani, a member of the Mikadono Group's Seiryuu Association, to assist him in the investigation.
After Konoe confessed to have been the one calling him, Miyabi came out with the revealation that the reason she couldn't attend Kumagorou's funeral was because of the Miryuuin entrance exam. This led Shougo to think that he might actually have a sister living somewhere else. However, his theory was proven wrong after he found out about Miyabi lying about said entrance exam being on that particular day.
Having finally cleared the past between him, Konoe and Miyabi, Shougo decided to confess his love to Konoe. The two of them would eventually marry with each other; while atthe same time, Miyabi's adopted father also married Kanoko, which meant Miyabi was now Shougo's step-sister.