I've never really gotten into the manga/anime culture. Not anything against it, I've just tended to gravitate to my more familiar American and European comics. Not to say I haven't seen the classics like Akira, but I haven't sought out much manga to read. But there is one series that I pick up as each new volume is released, and that is what is called here in the States Case Closed. Fun fact, the Japanese title is Detective Conan, but execs were concerned with possible confusion with Conan the Barbarian, so they chose the new title. Conan is many things, but I don't think detective is one of them. However, can't you see him starring in CSI: Cimmeria: "By Crom! The blood splatter patterns indicate the shot came from below the victim. Now I must go and tell his wife and daughters, and hear the lamentations of his women."
Case Closed is the story of Jimmy Kudo (and I apologize to all purists for using the anglicized character names, but it's how I am familiar with them), teen detective, who goes after a pair of mysterious men in black and is poisoned. Only the poison doesn't kill him. It instead de-ages him to about 8 years old. So he has the mind of a seventeen year old in an eight year old's body, and must find the men in black to hopefully find a cure while solving mysteries along the way. The series has been running for over fifteen years in Japan, and the volumes here in the States are only caught up about halfway, so I'm a bit behind.
Jimmy is a likeable protagonist, if a bit headstrong, which gets him into trouble like being poisoned by mysterious organizations. He is a deductive genius, more capable than nearly any other detective, but also is an excellent soccer player, and he uses those skills to sometimes aid in stopping criminals. The only person who knows his secret at the beginning of the series is Doc Agasa, am absent minded scientist who lives next door to Jimmy and who gives him various gadgets, including a pair of sneakers that strengthens his kicks to what they would be if he was his normal self, a pair of glasses that allow him to follow specially designed trackers, a bowtie that changes his voice to sound like anyone, and a watch that shoots darts that temporarily knock out people.
Jimmy takes the name Conan Edogawa, after Sir Arthur Conan Doyle, creator of Sherlock Holmes, and Edogawa Rampo, one of Japan's greatest mystery novelists, and begins living with Rachel Moore, his best friend and the girl that he was almost/sorta/kinda dating before his transformation, and her father Richard, a down on his luck drunken PI. Rachel is sweet, kind, and often worried about Jimmy, and while she occasionally is threatened by the criminals that are involved in the cases her father and Jimmy get into, she is a karate and judo expert, so she can handle herself. Richard is a drunk and a bit of a lecher, although he carries a torch for his wife, Eva, from whom he is separated, and while he isn't terribly bright, there are moments where the reader sees he's more clever than he usually seems. Conan accompanies Richard on cases and knocks him out with a dart from his watch and uses the bowtie to sound like Richard and solves the cases for him, earning Richard a reputation as a great detective with the moniker "Sleeping Moore," since he appears asleep when solving crimes.
Most cases over the course of series are either cases that Conan goes on with Richard, or ones he gets involved in with the Junior Detective League, a group of grade schoolers he goes to class with now that he's forced back into grammar school. At the beginning of the series, the the League includes George, the large not too bright member, bookish Mitch, and sweet Amy. Eventually, a new member is added, Anita, who is a former member of the Black Oranization who was de-aged in the same way Jimmy was, figured out Conan's true identity, and is also seeking a cure. Doc Agasa took in Anita, and he often serves as chaperon for the adventures the League gets into.
A cast shot from the anime, with Jimmy, Conan, Richard and Rachel in the center
I understand that the description I just gave makes things sound a bit contrived, with goofy scientist neighbors and drunken detectives just happening to be around when our protagonist conveniently needs them and doing things that are clearly outlandish. But once you get beyond the somewhat out of the normal setup, the series runs as a great collection of mystery stories. The majority of the crimes investigated are murders, although the cases with the Detective League can be a bit lighter on the gore. Evidence is laid out throughout each chapter, and the reader can play along, although I'll be honest, I'm more often than not stumped before Conan reveals how the criminal did it. It's also aware of its genre, with moments like Inspector Meguire, the main police officer, a Lestrade to Jimmy/Conan's Holmes, drawing attention to the fact that Richard and Conan seem to always be stumbling upon corpses, playing with the trope of Jessica Fletcher Syndrome (for those not familiar with the term, which finds its origins in the TV series Murder, She Wrote, it's when people tend to be murdered around a person on a regular basis).
One of the other joys I find in Case Closed is finding out the motives behind the various murders. While its understandable that the cases Conan winds up investigating are perpetrated in complex ways, since you don't need a super sleuth to solve a mugging gone bad, the motives are also usually as twisted as the method. No one gets wronged by a former employer or lover and just kills them the next week in Case Closed. A couple of my favorite examples are the man who blaims a doctor for not saving his young son's life, so he spends years sending the doctor his son's favorite toys so the doctor can give them to his son and then plans to kill the doctor's son when he's the same age as the dead boy, or the guy who blames a police officer for his mother's death during a chase when he was a boy, and so finds the officer's daughter when they're both adults, woos her, gets engaged, and then poisons her on the wedding day.
The mythology of Case Closed is complex, but it doesn't take over the series. The stories involving the Black Organization don't pop up too often, and the exact nature of their plans are revealed slowly; and there are various government agencies in Japan and the US who are hunting them, building a web of intrigue that Conan is in the middle of. But that mythology, while important, isn't what brings a reader back. The mysteries and the fun characters. The cast does grow beyond the initial characters, with new police officers and allies added, and they're all memorable, from Harley Hartwell, another teen detective who starts out as a rival to Jimmy but after deducing Jimmy's identity as Conan becomes a stalwart ally, to Miss Jodie, one of Rachel's teachers who has a mysterious past.
While much of the subject matter is dire, with corpses popping up and Conan constantly in fear of the Black Organization finding out he is still alive and killing him and all he loves, there is a healthy dose of comedy. Richard is bumbling, and his usually outlandish theories and arrogant demeanor are a source of a lot of comedy. Conan occasionally gets into situations where his more adult mind is even more at odds with his body, usually when he is with Rachel, who doesn't know he's Jimmy. And the Junior Detective League stories often have a lighter touch, with childish hijinks; the interactions between the kids is well written, and is especially amusing when seen through the eyes of Conan, who has to act like a little kid even though he is anything but.
Forty four volumes of Case Closed are available here in the US currently, translated into English from Viz Media, with new volumes coming out quarterly. Also, at least five seasons of the anime and a few of the animated features are also available, dubbed, here in the US from Funimation.