Iori Arai is the infant son of the swordsmith Arai Seiku and his wife Azusa, living a quiet life on the outskirts of Kyoto. As the grandson of the legendary swordmaker Arai Shakku, he is part of a family with a profound history tied to the violent era that preceded the Meiji period. Iori is a happy and friendly child who, having known only peace, seems to enjoy the presence of everyone he meets. He has a charming habit of giving people nicknames based on their most obvious physical or verbal traits.

When the wandering swordsman Himura Kenshin arrives at his father's workshop seeking a new blade, Iori immediately takes a liking to him. Fascinated by the polite suffix Kenshin often uses, the child nicknames him Gojaru. This lighthearted bond demonstrates Iori's open and perceptive nature, as he identifies people not with suspicion, but with innocent creativity.

The central role Iori plays in the story begins when he makes the acquaintance of Sawagejo Cho, a flamboyant and ruthless member of the Juppongatana. Iori initially nicknames Cho broom for his tall shock of light-colored hair, and he is thrilled by the attention of the strange man. However, this quickly turns to fear when he realizes that Cho is using him as a hostage to blackmail his parents into revealing the location of his grandfather's final and most powerful sword. Iori is kidnapped and brought to Hakusan Shrine, terrified and crying, yet his spirits lift the moment he sees Gojaru waiting to rescue him.

While Kenshin and Cho battle at the shrine, Cho places Iori in a tree for safekeeping. Rather than cowering, Iori watches the fight with gleeful excitement, cheering for Kenshin as the two swordsmen clash. This moment reinforces his role as a symbol of the new era he knows nothing of bloodshed and can therefore witness a battle as a spectacle rather than a tragedy. After Kenshin defeats Cho, Iori is safely returned to his parents, seemingly unharmed by his ordeal.

The nature of Iori's relationships is defined entirely by his innocence and vulnerability. He is deeply loved by his parents, Seiku and Azusa, who are driven to desperate measures to ensure his safety. His grandfather, Shakku, died before Iori was born, but the last sword he created was made with the hope that a grandchild he would never meet could live in a peaceful world. Iori's interaction with Kenshin is one of pure trust and gratitude; he is unaware of Kenshin's past as the Hitokiri Battousai and simply sees him as a kind protector. His relationship with Cho begins with childish fascination but turns into fear after he is taken hostage.

Iori does not develop over the course of the story as he is a very small child. His purpose is not to change but to act as a catalyst for others and to represent a thematic ideal. His existence represents the peaceful new era of Meiji, a living symbol of hope for a future free from the battles and bloodshed of the past. It is for the sake of this future, represented by Iori, that Kenshin refuses to kill even when fighting to save the child. As an infant, Iori has no notable combat abilities or special skills. His most significant traits are his charm, his perceptiveness in reading the emotions of adults, and his talent for creating memorable nicknames based on simple observations of those around him.