Iris Watson is a character in the Dai Gykauten Saiban games. At just 10 years old, she is a child genius, having a medical PhD, and being the publisher of "The Adventures of Sherlock Holmes". She is the daughter of John H. Watson, and lives with Sherlock Holmes at 221B Baker Street. Unfortunately, while he's on a trip to Japan, her father is murdered by a fellow visiting Briton, and the Japanese university student Ryūnosuke Naruhodō is falsely accused of his murder.
After his acquittal and subsequent journey to Great Britain, Ryūnosuke had a run in with Sherlock Holmes, and ultimately ended up befriending both him and Iris, who allowed him to live in the 221B attic. She aided him during one of his cases when he was defending Gina Lestrade, who was accused of the murders of two men, plus the non-lethal stabbing of Holmes.
Despite her genius, she still very much acts like a child, and has the same mindset as one during most situations.