Here's how to request your favorite manga to be published in English. Let's manifest some licenses!
Besides making noise on social media, here's how to let English publishers know that you're interested in reading a manga or two!
Bookwalker is an e-store based in Japan that distributes manga, light novels, and audiobooks worldwide. You can request a new license via the Contact Us/Request Books link in the footer of the homepage.
Before the big rebrand and website change in March 2021, Kodansha used to have a link on their website where you can directly request manga. Now that the website has changed, I don't see it anymore. However, I did find an old official FAQ Tumblr post about what they license and why. Kodansha's Tumblr is mostly inactive now, but Kodansha is active on Facebook, Twitter, Instagram, and YouTube.
One Peace Books (https://www.onepeacebooks.com/index.html)
You can request new manga from One Peace books via the Contact Us page. Scroll to the very bottom of the Contact Us page to find this form:
ShojoBeat is VIZ Media's dedicated shojo imprint. The brand boasts "Stories from the heart. Character-driven romance, fantasy, and comedy for teens and adults from the leader in shojo manga." The brand has dedicated socials, and ShojoBeat takes requests for manga on its Tumblr page.
SuBLime is a dedicated Boys Love imprint of VIZ Media. The brand has its website and socials. You can request boys love manga via the Google Form on the FAQ page. (Note the site is 18+ and NSFW!)
Seven Seas (https://sevenseasentertainment.com/)
Seven Seas has a new manga survey every month. The survey asks for information about your buying habits (ex: do you read digitally or physically?, What Seven Seas books are you excited for? etc.) along with what manga/manhua/manhwa/webtoon or novel/light novel/danmei that you'd like to see licensed. You can find it on the front page of their website. It will always be in the top right corner under the search bar. Seven Seas also shares the survey on Twitter and in their newsletter.
Star Fruit Books (https://starfruitbooks.com/)
Small indie publisher Star Fruit Books takes manga requests on their website. You can find the link in the About drop-down menu or the footer of the website.
VIZ is a little tricky. On the home page, scroll down to the bottom and click "Contact VIZ."
On the Contact VIZ page, you'll see a drop-down menu. From the drop-down menu, click "Series Suggestion."
Before you start requesting licenses, you may need to look up the Japanese title, the Japanese publisher and magazine, and the year the title was published. You can find this information on databases like MangaUpdates, MyAnimeList, or a general Wiki/Google search. Also, you might want to check out the manga the publisher already licensed to better your odds. For example, VIZ is owned by Japanese publishing conglomerates Shueisha and Shogakukan so don't ask them to publish manga from Kodansha-owned and published magazines like Kiss or Dessert. Ask VIZ to publish manga from Shueisha and Shogakukan magazines like the Shonen Jump, Shonen Sunday, Big Comic Superior, Cheese!, Betsucomi, Margaret, Flowers, etc. Finally, keep in mind that some manga may be too niche, too old, or too "risky" to publish as pointed out in this AnimeNewsNetwork Answerman post from 2018, but it doesn't hurt to ask. Miracles can happen. (Stares pointedly at Usotoki Rhetoric. I have no clue how this happened, but I'm ecstatic!)
This is all the licensing information that I can find at the moment. Let's manifest some licenses!