Daikoku Nikaidō is the older brother of Kaho Nikaidō, the female protagonist. He is a 29-year-old man with a masculine build, red eyes, and blue hair that reaches his waist. His most defining personality trait is his extreme and obsessive love for his younger sister. What initially appears to be a typical, caring protective attitude quickly reveals itself as an intense, over-the-top obsession. He is known to collect items that Kaho has used and seal them in plastic bags as keepsakes, demonstrating the extent of his fixation. This behavior categorizes him as a super brother-con, or someone with an excessive, romanticized devotion to a sibling.

Daikoku’s primary motivation is to safeguard Kaho’s well-being and purity, often to a comically unreasonable degree. He is deeply suspicious of anyone who gets close to her, particularly romantic interests. Before his introduction, Kaho believed her brother was studying in America, maintaining a seemingly normal and kind relationship with him through letters and phone calls. This made his true, eccentric nature a shock to her when he reappeared. Within the story, Daikoku serves as a secondary character whose primary role is to create comedic conflict. His overprotective antics act as an obstacle for Kaho’s relationships, turning typical familial concern into a source of humor due to its sheer absurdity.

In terms of key relationships, his entire world revolves around his sister, Kaho. His interactions with other characters are almost entirely filtered through his perception of them as potential threats to her. While he appears late in the series and does not have a significant amount of screen time compared to the main cast, his presence is impactful during his appearances. There is no substantial information available about his development throughout the series or any notable abilities he may possess.