Nico Robin, also known by the code name Miss All Sunday or Srta. Domingo during her time with Baroque Works, is a central character who serves as the archaeologist of the Straw Hat Pirates. She was born on the island of Ohara in the West Blue, a place renowned for its vast library and community of scholars. Her mother, Nico Olvia, left when Robin was very young to search for the world's lost history, entrusting her to relatives. Robin displayed exceptional intelligence from childhood, earning a doctorate in archaeology at the age of eight and secretly learning to read the ancient stone tablets known as Poneglyphs—a skill considered forbidden by the World Government. When the World Government learned of Ohara's research into the Void Century, they launched a devastating Buster Call that destroyed the island and killed nearly everyone, including Robin's mother and the scholars. Robin was the sole survivor, saved by the giant Jaguar D. Saul, who urged her to live and carry on the scholars' mission. For the next twenty years, she was hunted as the "Devil Child" and forced to survive by her wits, eventually joining the criminal syndicate Baroque Works as the vice president under the alias Miss All Sunday.

Robin's personality is marked by a calm, reserved, and highly intelligent demeanor. She is often seen reading and possesses a dry, sometimes morbid sense of humor that contrasts with her more outwardly emotional crewmates. Initially, she kept others at a distance, having learned from a lifetime of betrayal to rely only on herself. However, after joining the Straw Hat Pirates at the end of the Arabasta arc, she gradually learned to trust and open up, finding a sense of family and belonging she had never known. Her primary motivation is to uncover the true history of the world, particularly the events of the Void Century, by reading the Rio Poneglyph—a collection of stone tablets that, when assembled, reveal the world's lost history. This goal honors the sacrifices of her mother and the scholars of Ohara and drives her to help the Straw Hats reach the final island, Laugh Tale.

Within the story, Robin plays a vital role as the crew's archaeologist, deciphering Poneglyphs that guide their journey and reveal secrets about the ancient weapons and the world's past. She is also a formidable combatant using her Devil Fruit powers. Her key relationships include her deep bond with Luffy, who accepted her unconditionally and saved her from despair during the Enies Lobby arc—the turning point where she openly declared her desire to live and stay with her new family. She shares a close friendship with the other crew members, especially Nami, and maintains a connection to the Revolutionary Army through her former association. Under the giant Jaguar D. Saul's protection and the mentorship of Professor Clover, Robin's development centers on moving from isolation to embracing camaraderie and hope, a transformation symbolized by her iconic moment at Enies Lobby.

Her notable abilities stem from the Hana Hana no Mi, a Paramecia-type Devil Fruit that lets her sprout replicas of any part of her body from any surface. She can create multiple limbs for combat, espionage, or support—growing eyes and ears to spy, arms to restrain opponents, or gigantic limbs for powerful strikes. She can even generate full clones of herself. Beyond her Devil Fruit, her scholarly knowledge of history, ancient languages, and archaeology is unparalleled in the world. Her bounty has risen significantly over the course of the story, reflecting her increasing importance and the threat she poses to the World Government: from 79,000,000 berries after Ohara to 930,000,000 berries after the raid on Onigashima. Robin's journey is one of survival, discovery, and the redemptive power of trust, making her an indispensable and deeply layered member of the Straw Hat Pirates.