The character name "Reiko O'Hara" may seem intended to be incongruous, but, in fact, "Ohara" (without the apostrophe) is a not uncommon Japanese family name (actor Pat Morita starred as police lieutenant Ohara (1987) in the eponymous TV series). "-hara" is an ending shared by a fair number of Japanese names (e.g.: "Fujihara" or "Sinohara").
The title refers to the Japanese warrior nobility class of the 7th to the 19th century.