This is another one of those general posts, where I ramble on about the industry in general rather than a specific title. In this post, I talk about the various companies that put out manga in Japan, and what, if any, relationship they have with North American publishers. This might help people who ask publishers "Why don't you get title X", not realizing that title X is owned by a Japanese publisher who is exclusive to someone else. I've written this post before on my Livejournal, but am revising it to post here, even though I know I risk various industry people commenting on how wrong I am. They are welcome to do so, of course. I freely admit I have no 'inside information'. Also, few Japanese publishers are actually 'exclusive'; most merely have strong working relationships, a phrase you'll find me using constantly below.
I tend to define Japanese publishers into three categories: The Big Four, The Mid-Majors, and other. Technically speaking in Japan I think it would just be The Big Three, but Hakusensha is enough of a powerhouse over here that I think it deserves a place with the big boys.
Let's start with Shueisha, which puts out, among other things, everything with 'Jump' in the title (shonen and seinen comics) and everything with 'Ribon' and 'Margaret' in the title (shoujo comics). They are part-owners of Viz, and for the most part they license exclusively to Viz, with one or two exceptions (Gantz, a Shueisha title, was licensed to Dark Horse, most likely as DH could do a much better job pushing it over here; also, in the old days, Viz let Tokyopop license two popular Shueisha shoujo titles, Marmalade Boy and Kodocha).
The other co-owner of Viz is Shogakukan, who have the 'Sunday' titles and everything with 'Big Comic' in it (shonen and seinen), and the shoujo and josei with 'Comic' in it (aka Shocomi and Betsucomi). They too are mostly exclusive to Viz; the one or two exceptions I've seen have been where the author owned his own rights and could choose the publisher (Darren Shan/Cirque Du Freak, a Sunday title being published by Yen Press; Moto Hagio just licensed her work to Fantagraphics; and I think that the Fanfare/Ponent Mon Taniguchi titles were also Shogakukan titles.)
Kodansha is the other Japanese heavy hitter, having the boy's and men's titles with 'Magazine' in them, the men's titles based around times of the day (Morning, Afternoon, Evening), and the women's titles that don't fit a pattern, Betsufure/Nakayoshi/Be Love. They are trying to start their own imprint in North America, but so far have not really done much. In the meantime, they have a strong relationship with Del Rey, which puts out the majority of Kodansha titles today. They still work with Dark Horse, both with the old Oh My Goddess and Gunsmith Cats licenses, and via the newer agreement with CLAMP. They have also started to license a few titles to Vertical. They used to have a strong relationship with Tokyopop as well, but Kodansha pulled the rights to those titles a few years back. Again, note the exceptions are 'author controls where his or her work goes' - Vagabond, a Kodansha title, is published by Viz.
Hakusensha is the largest Japanese publisher that does not have a strong relationship with any one publisher over here, preferring to sell its shoujo (and occasional seinen) titles to whoever wants to license them the most. As a result, three NA publishers have good relationships with the company; Viz, Tokyopop and CMX. And all three, in fact, have had titles that have made their company wildly successful; Viz with Vampire Knight, Tokyopop with Fruits Basket, and CMX, while not receiving much financial success, has quietly gotten praise for much of its entire line of small Hakusensha titles.
That's the big four, but that still leaves a lot of publishers. Let's look at some of them:
Akita Shoten has its Champion titles for boys and men, and its Princess titles for girls. It too does not limit itself to one publisher, licensing many titles to Go! Comi, DMP, Tokyopop, Yen Press, and CMX. Akita Shoten also has bought the license to reprint many old Shueisha and Hakusensha titles, putting them back in print in Japan after a long period - and also, coincidentally, licensing them over here. CMX's Swan, which was originally a Shueisha title in Margaret, was bought by Akita Shoten. They also have the cult 'license request' title Sukeban Deka, originally a Hakusensha title.
ASCII Media Works is where you get all the Dengeki titles, including the most well-known, Dengeki Daioh. They've worked with Viz, Tokyopop, Seven Seas, Dr Master, Bandai, ADV Manga, and Yen Press, so they're fairly widespread.
(A quick note that when I say someone 'works with' Bandai North America, that usually means that Bandai Japan had the license to the title in the first place, and the manga rights never rested with the magazine. Some of the Gundam titles, Lucky Star, and Gurren Lagann apply here.)
Enterbrain is a new up-and-comer on the mid-major circuit, and have recently made waves over here with titles from their men's manga Comic Beam. They don't have much out over here, but when they do, they tend to work with CMX (Emma is theirs, as is King of Thorn). They also just licensed a title to Fantagraphics.
Gentosha is a small publisher who has a seinen magazine, Comic Birz, which has seen some titles over here, as well as two yaoi magazines that have seen even more. They seem to have a strong working relationship with Tokyopop.
Houbunsha has recently found a great deal of success in the 4-koma market; many of their successful titles are based around that, and have spun off into equally cute if pointless anime series. They have a good working relationship here with Yen Press.
Ichijinsha has a boy's comic, Zero-Sum, from which it usually licenses titles to Tokyopop. Their yuri magazine Yuri Hime had a relationship with Seven Seas at one point, but it seems to have ended.
Jive is a small publisher with only one major magazine to speak of, the otaku-oriented Comic Rush, but it's also notable as the biggest publisher to license to Broccoli back when Broccoli was in the North American market. Their Jive magazine also licensed the adult Maka-Maka to Media Blasters.
Kadokawa Shoten has a strong working relationship with Tokyopop, but has also used a number of different publishers to put out its titles (usually with Ace in them for men, and Asuka for women). They've also licensed to Viz, Dark Horse, and Bandai. There's also Fujimi Shobo, which is a Kadokawa offshoot (The magazines have 'Dragon' it the title); they've licensed those to ADV, Viz, Tokyopop and CPM (the Slayers line).
Libre Publishing, which arose out of the remains of Biblos. Probably the biggest licensor of yaoi to North America, and the publishers they work with are many and varied. They've worked with Aurora, DMP, and Tokyopop; Biblos used to work with CPM.
Mag Garden has its various Comic Blade titles, both for boys and girls. After a brief relationship with ADV died when ADV's manga division did, they've since formed a strong working relationship with Tokyopop, which I believe is almost exclusive; I haven't seen Mag Garden titles going anywhere else these days.
Media Factory is a publisher with two small but cult-popular men's magazines. They also have a large number of titles for the gaming and 'moe' market. They've worked with Dark Horse, CMX, Vertical, and Tokyopop.
Shinshokan has the magazine Wings, which is not-quite-shoujo, not-quite-yaoi, not-quite-fantasy, but very... whatever Wings is. It's licensed to Go! Comi, DMP and Tokyopop.
Shodensha has the women's magazine Feel Young, but that's quite a powerhouse in women's magazines in Japan. It's licensed here to Tokyopop, and recently to Yen Press.
Shonen Gahosha is known here for the magazine Young King OURS (Young King, its parent magazine, is more popular in Japan but its titles tend to be a bit too 'manly' for North America). It has a strong working relationship with Dark Horse, and has also licensed to Viz, Dr. Master, and CPM.
Square Enix is one of the larger mid-majors, up there with Akita and Kadokawa. Their Gangan line has pretty much exploded since beginning in the early 90s, and they now have several spin-off magazines. They used to work primarily with Viz, but when Yen Press started, they began a strong working relationship with Square Enix, via their Yen Plus magazine. The majority of the Square Enix titles I see these days are via Yen.
In addition to these, CMX has an agreement with a Japanese publisher called Flex to co-develop titles; I believe that Flex's market in Japan is for the portable iPhone manga crowd.
That's all the ones I can think of; if you have a Japanese publisher that puts out a number of titles here, let me know (I admit I'm not as familiar with the yaoi market). To sum up, you can't just ask a North American publisher to license title X without knowing a) which Japanese company put it out; b) which Japanese company owns it now; c) whether an author controls their own rights; and d) which publishers work with which companies. I hope this list helps you with d, if nothing else.