Hello, I tried to send a fan letter to Hiromu via her publisher but It looks like I had the address wrong. Where should I send it to? Thank you for your time. - Bobby Bowden
I hope you don’t mind me answering this publicly (please tell me if you do), but I thought maybe other people would be interested.
According to the Shounen Sunday magazine, this is their fanmail address for any mangaka who works for them:
〒119-0141 Tokyo, Chiyoda-ku, Hitotsubashi 2-3-1
Shogakukan Shonen Sunday
If you’re mailing internationally, remember to write “Japan” somewhere too. And don’t forget to include Arakawa’s name and the series she’s currently working on, just in case: 銀の匙 / 荒川弘先生 or Gin no Saji / Arakawa Hiromu sensei.
In addition, Web Sunday also has an email form where you can send messages of encouragement to their mangakas right here. Just choose 荒川弘 in the dropdown box and fill the form with your message (メール本文), name (あなたのお名前) and, just if you want, age (年齢). Then click on the bottom right submit button.
You can also try through Hyakushou Kizoku's magazine, Wings, and its publisher, Shinshokan. This is their address, as far as I've been able to find:
〒113-0024 Tokyo, Bunkyo-ku, Nishikata 2-19-18
Shinshokan Ltd. Wings Editorial Department
Again, be sure to include “Japan” and the recipient: 百姓貴族 / 荒川弘先生 or Hyakushou Kizoku / Arakawa Hiromu sensei.
Be aware that I’m not 100% sure these are correct (or even work!) and that, most likely, you won’t get any response anyway. I hope this is still useful though!