GUIDE TO CONVERT AOZORA BUNKO TEXT FILES INTO MOBI EBOOKS
1. Download a book that's in 青空文庫 format (text file LNs are usually in this format already).
2. Download and extract AozoraEpub3 (Java required). Link: http://www18.atwiki.jp/hmdev/pages/21.html
3. Download and extract Kindlegen. Link: http://www.amazon.com/gp/feature.html?docId=1000765211
4. Put "kindlegen.exe" on the AozoraEpub3 directory.
5. In the 変換 tab, select the format ".mobi" from the 拡張子 dropdown list.
6. Click on ファイル選択 and select the text file(s) you wish to convert and specify the output directory.
7. A window will appear with options for the title, author, table of contents and image metadata. Configure them as you want.
8. Once you're finished setting up the metadata, click on 変換実行. This will generate a mobi file.
This will result in a non-searchable ebook that is just fine if you're okay with not being able to look up words comfortably because the Kindle selects the whole sentence at once.
If you want to make them searchable, follow the steps here: http://pastebin.com/qdaYzitJ