Which themes are available and how do I obtain them?

The following themes are available from official worldwide launch on April 10: 

FINAL FANTASY VII REMAKE Sephiroth Theme
This is a pre-order bonus at selected regional retailers. Please find a non-exhaustive list of retailers below:

UK, Germany, Spain, Italy – Amazon
France – Micromania
Australia & New Zealand – Mighty Ape
Norway, Sweden, Denmark, Finland – Webhallen
Latvia, Lithuania, Estonia – Euronics, PSX.LV
Poland, Czech Republic – Empik, JRC, Media Markt, Xzone, MediaExport
Portugal – Fnac
Romania – Ozone BG
Russia – Mvideo
South Africa – BT Games