What you need:
1. xclannad (from http://cydia.myrepospace.com/snipelimited/)
2. A Key visual novel already installed to your PC (e.g. Clannad)
3. A jailbroken iPad/iPhone/iPod Touch
4. i-FunBox (preferred method to transfer files from PC to iOS)
5. seen.txt, GAMEEXE.INI and default.tff
How to install:
1 – From your iDevice, Open Cydia and click on “Manage”
2 – Click on “Sources” and add this source: http://cydia.myrepospace.com/snipelimited
3 – Click on “Search”, find and install xClannad.
4 – Open i-FunBox on your PC and connect your iDevice to it.
5 – Create a folder in “var/mobile/Media” and name it “ons”. Then create another folder in “ons” and name it “clannad”.
6 – Transfer all these folders from the game you want to play into “var/mobile/Media/ons/clannad”:
7 – Transfer these files into the same directory as well:
default.ttf (You can use any font but make sure to rename it to default.ttf)
8 – Now safely remove your iDevice from your PC and start playing!
Notes: So far I’ve tried playing Clannad and Little Busters! and they run prefectly well on my iPhone 3G. Little Busters would cause an error during the baseball mini-game, though.
Notes 2: Another way to install xclannad is to download the .deb package from here. Open i-FunBox on your PC and connect your iDevice to it. Then copy the Clannad.deb file into the “Cydia App Install” folder. Once done, safely unplug your iDevice, reboot and respring it. After that, just continue from step 4 onwards as described above.