/HHN-C:-18@32F0F:game.exe - for ITH
/HXHN-C:-18@32F0F:game.exe - for AGTH v2011.4.21
Note that /HH codes are only supported by ITH and "previous stable version: 2011.4.21" of AGTH (not the latest v2011.5.9).

However, this will not give you Japanese text. The game doesn't use any hookable character encoding (Shift-JIS, UTF-16 or UTF-8), so it's impossible to extract text, but it's possible to extract character codes and then decode them with a conversion table made specifically for this game and a third-party tool. I'm working on a conversion table, but it's so time consuming that it will take a while.

The end result will consist of SavedReplacements.txt file for Textractor's Replacer plugin and Default.names.txt file for TAHelper; ITH/AGTH will copy character codes to the clipboard and Textractor or TAHelper will replace each character's code with Japanese character. For example, ITH will hook a series of numbers like 000001DD (AGTH will hook only 01DD) and Textractor's Replacer will change that to あ if strings |ORIG|0000|BECOMES||END| and |ORIG|01DD|BECOMES|あ|END| exist in SavedReplacements.txt. In a similar fashion TAHelper will remove 0000 and replace 01DD with あ.

On a bright side, once the table is complete, it will likely work with the fandisk or even other games on the same engine.

Edit: better H-code(s).

Edit 2: about 90% complete conversion table, for TAHelper only since it's still a WIP and it's easier to edit the table in TAHelper while playing the game.
Download TAHelper, run it once and exit, then replace newly created Default.names.txt file with the attached one.
Attach ITH (ITH3-win10CUfix if you play in Windows 10) or AGTH (preferably) to the game, make it copy characters codes to the clipboard, and TAHelper will replace them with Japanese if possible (tick "Enable" and "Replace all names" checkboxes in TAHelper).

Some characters will not be replaced because they are not in the table, feel free to recognize and add them yourself.
Please report wrongly converted characters, if there are any! Do not report missing characters, I will gradually add them in the following days as I play through the game.
The remaining 10% will probably take as much time to finish as previous 90% so I've decided to share what I have now and update it periodically as I verify more characters.

Edit 3: the fandisk is uploaded and cracked in a nearby thread, H-code(s) for that game are:
/HHN-C:-18@DFB28:game.exe and /HXHN-C:-18@DFB28:game.exe - ITH and AGTH respectively. Use the same versions of ITH and AGTH as you're using with the base game, and the same conversion table attached below.

Now all that's needed to complete the collection is Yuzuri After DLC. Hopefully it will be shared and cracked too.
(The mods can't be arsed to do their job and approve my posts in the fandisk's thread for like 5 days already, so I have to use this one for both games. Why is this forum so fucked up, even abandoned and spam-filled Hongfire was better because at least it allowed people to post. Bring it back, someone)

A mirror of conversion table for unregistered users:
http://s000.tinyupload.com/?file_id=38921946058487591051

Anonymouse

http://www.anime-sharing.com/forum/miscellaneous-45/%5B%E4%B8%80%E8%88%AC%E3%82%B2%E3%83%BC%E3%83%A0%5D%5Bmages%5D-%5B280318%5D-%E3%83%A1%E3%83%A2%E3%83%AA%E3%83%BC%E3%82%BA%E3%82%AA%E3%83%95-innocent-fille-memories-off-innocent-fille-jp-907844/#post5100009