Shijuro Ohara (大原 四十郎) is Nanako's father. He is a famous author of many popular books. He is overprotective of his daughter and worries too much about her. He is often seen to disrupt any important matters at hand whenever he has the most extremely subtle (false) hint that Nanako may be in trouble. He disapproves of Shin-chan's love for his daughter though they both band together in keeping an eye on her.
In both the anime (episode 274a) and manga Nanako's mother/Shijuro's wife appears (although her name is unknown).
His first appearance is in episode 236c. In this episode he has a different appearance to his appearance in later episodes of the anime.