The pseudonym EDOGAWA Rampo (江戸川乱歩 1894-1965) is one of those exceptions, known abroad with the Japanese name order, perhaps in order to preserve the punning reference. (Or is there some reason I don't understand? The Japanese Wikipedia regularly refers to him as Rampo, which would be an unusual use of the given name; but apparently obvious pseudonyms are treated differently.) He is one of the most influential figures in Japanese crime writing, with stories in a variety of subgenres. The best known are probably those which have an emphasis on horror and abnormality, a trend in Japan at that time. I have only read two short stories, both more classical mysteries (and both excellent): D坂の殺人事件 (The D-Slope Murder Case 1925) and 二癈人 (Two Invalids 1924). The first of these is a locked room mystery of sorts, at least it is presented as such by the narrator, whose judgement is not terribly reliable. But in a few pages it runs assuredly through innumerable familiar tricks of detective fiction, turning them on their heads. (Often when reading puzzle detective stories, I've thought, 'You know, there've been some quite thorough demonstrations of the unreliability of eye-witnesses. Someone should write a story with awareness of that research.' I hadn't realized that it had already been done in 1925.) It's also the first appearance of Edogawa's series detective, AKECHI Kogorou (明智小五郎), who is also the hero of the book in the title to this post.
The Fiend with Twenty Faces (怪人二十面相 1936) is the first in a series of adventure stories for children. The title character is a brilliant thief, able to disguise himself perfectly. He is currently busy collecting the fine art and other treasures of the richest families in Japan, always sending a letter ahead of his attack, to let them know that they are about to be robbed. Appropriate to a story for children, he has a strong dislike for shedding blood; and the gun he carries on his first appearance is a toy. For the first half of the book Akechi is out of the country, but his assistant, the twelve year old KOBAYASHI Yoshio (小林芳雄) stands in for him, with incredible self assurance.
Soutarou entered the room and found a boy of twelve or thirteen, with apple like cheeks and large eyes.
"Mr. Hashiba? Pleased to meet you. I'm Kobayashi of the Akechi Detective Office. Since you were so kind as to telephone us, I've come to discuss things."
The boy spoke distinctly, his eyes large and alert.
"Ah, you're Mr. Kobayashi's assistant? It's a rather complicated case, you know. I would prefer to speak to the man himself ...."
The boy put his hand up as if to stop Soutarou, and replied, "No, I'm Kobayashi Yoshio. There's no other assistant but me."
The self confidence is fairly well justified, particularly as, in contrast to the villain, Kobayashi is equipped with a real gun. But of course Twenty Faces remains at large to escalate his threats in the second half of the book, with an attempt to steal all the art works of the National Museum.
This is broadly written adventure aimed probably at readers slightly younger than Kobayashi. Towards the end of the book, Kobayashi gains a group of allies, the Boy Detective Club, who are about ten years old. It's easy and amusing reading, though the twists are signalled more obviously for the book's young readers. The gleeful lack of sophistication in the writing is one of the book's strongest qualities, emphasising the writer's awareness of his readers, who are addressed directly, and invited to speculate or react to the events described. In addition, the background of prewar Tokyo adds an extra interest for modern readers. For instance, the suspicious figure of a kamishibai man is actually one of Twenty Faces henchmen, observing Akechi's house.
For once, there is an English translation. I haven't read it; so I can't speak for its quality. (I will say I hate the cover, which is not my idea of the book at all.) At least the few reactions to it that I can find online are positive.