Bô, also known as Bo-chan, is a five-year-old boy and a classmate of Shin-chan Nohara in the Sunflower class at Futaba Kindergarten. He is a member of the Kasukabe Defense Force, the group of friends at the center of the story's adventures. His real name is largely a mystery, though a tournament bracket once listed him as Igawa Bōtarō, a name that has not been confirmed as his true identity. He was born on September 10th.

Bô presents a deceptively simple exterior. He is known for speaking very slowly and often appears to be daydreaming or unengaged, with a perpetually blank expression. However, this sleepy demeanor masks a sharp and surprisingly intelligent mind. He frequently offers insightful observations and practical knowledge that astonish his friends, and he has a deep curiosity for artistic, intellectual, and adult-oriented subjects. Bô is exceptionally calm and composed, rarely losing his nerve even in chaotic or dangerous situations, and acts as a quiet pillar of stability within his friend group. He is kind, polite, and helpful, often stepping in to support others without seeking any recognition.

The most defining aspect of Bô's appearance is the trail of mucus that constantly hangs from his nose. Far from being a simple bodily function, he has remarkable control over it, using it to perform tricks and even as a makeshift weapon in dire situations. He is deeply attached to it, as its removal disrupts his sense of balance.

Bô's primary motivation stems from his quiet passions. He is an avid collector of unusually shaped stones, claiming to know a secret place in Japan where the rarest examples can be found. He is also fascinated by urban legends, UFOs, and other mysterious phenomena. In free play, he almost always volunteers to take on the role of a pet dog or cat. He dreams of a variety of unusual careers, including a pilot, a visual rock band lead singer, an artist, and an inventor, and he aspires to one day open his own museum dedicated to his stone collection.

Within the Kasukabe Defense Force, Bô plays a unique and invaluable role. He is often considered the secret weapon of the group due to his hidden talents and unshakable resolve. His most significant relationship is with Shin-chan. Among all their friends, Bô is the one who most readily understands and accepts Shin-chan's bizarre behavior, enthusiastically joining in his imaginative and often nonsensical games. He is a good friend to the timid Masao, often comforting him when he is upset, and shares a supportive friendship with Nene. He and the more serious Kazama are also close, though Shin-chan occasionally teases Kazama by suggesting Bô is actually the more intelligent of the two.

Bô's family background is an enduring mystery. While it is known he has a mother and father, his father has never appeared, and his mother has only been shown once, with her face obscured. An older sister has been alluded to, and his grandmother has been confirmed to exist. Despite the lack of detail about his home life, the other defense force members eventually learn where he lives. He also owns a pet snail named Tsumuro.

Throughout the series, Bô demonstrates a range of notable abilities that go far beyond his slow-speaking exterior. In addition to his control over his nasal mucus, he has exhibited surprising technical knowledge, such as knowing how to start a motorboat and recognizing the number of stitches on a baseball at a glance. He is also capable of reading complex kanji and has expert-level calligraphy skills. His ability to seemingly fade into the background, making his presence disappear, is another unique trait. In the feature films, these skills become even more pronounced; an adult version of Bô fulfills his dream of becoming an inventor, piloting a giant combat robot. While he rarely seeks the spotlight, his courage, intelligence, and versatility consistently prove to be essential to his friends, even earning him the quiet respect of Shin-chan himself.