It's hard to talk about the mystery genre without at least mentioning the influence of Sir Arthur Conan Doyle's Sherlock Holmes. It's like trying to talk about anime without mentioning Dragon Ball Z or video games without Super Mario Bros. However, at some point, it stops becoming an homage and just turns into a trope. Numerous mystery anime have fallen back on this trope and honestly, it's gotten stale.
Since his first appearance in 1887's A Study in Scarlet, Holmes has captivated mystery-lovers for over a century. Holmes' attention to detail, his miraculous deductions from seemingly innocuous things and his rivalry with Professor Moriarty have become the subject of many adaptations. Because he is so well-known and most likely the most famous fictional detective of all time (sorry, Batman), it's easy for people who know nothing about mysteries and detective stories to recognize the character. The deer-stalker cap, tweed suits, Inverness cape and pipe are always the outfit of choice when someone wants to recreate Sherlock Holmes -- it's just so recognizable.
Series like Moriarty the Patriot, Holmes in Kyoto and Case File nº221: Kabukicho all feature Holmes in some form or at the very least are derivative in some fashion. The long-running Case Closed (Detective Conan in Japan) even has its main character take on the name Conan, as in, Arthur Conan Doyle, and cites Sherlock Holmes as his inspiration for becoming a detective. However, at some point, relying on Holmes and Doyle becomes played out. Some of the best mystery series don't even try to recreate the sensation that was Sherlock Holmes. Monster and Another are two of many series that were able to craft interesting mysteries without falling back on the English detective.
Japan's fascination with Sherlock Holmes may come from an interest in foreign storytelling and characters. It's not the only country guilty of rehashing the same idea, and it won't be the last. But when series rely on something being called "The Best" of a genre, it doesn't stand out anymore. It becomes another derivative piece of media that uses a popular staple to try and legitimize its title as a mystery.
If a creator wants to make a mystery, they need to rely on their own talent and ideas rather than that of someone else, even if they take inspiration from an outside source. It's hard considering the amount of people in the world, and nothing is really original anymore, but that doesn't mean that we should fall back on hoping people will like something because it has Sherlock Holmes in it. At some point, it stops being its own thing and just becomes another drop in the bucket of Sherlock Holmes series. While it's fine to take inspiration from the series, relying on the name and character just comes off as a lack in confidence that the series can stand on its own.
