What the bot should do eventually (please discuss):
- Go through all the pages transcluding Template:Infobox animanga/Header.
- Remove the demographic tag from the header and save it in some buffer space.
- If that tag consists of exactly one demographic indication, copy that indication in each manga box, if any. Otherwise, keep track of the page for subsequent manual intervention.
- Make sure that the article belongs to the right categories once the changes are made.
See User:Bikabot for details.