Bandai Namco just made the free demo of Tales of Berseria available on the Japanese PlayStation Store.
The demo can be downloaded here (of course a Japanese PSN account is necessary to download and install the demo), and it requires only a 320 megabytes download. It includes a scenario mode and a battle mode, focused story and combat respectively.
Tales of Berseria, will be released on August 18th in Japan for PS4 and PS3, and early next year in the west for PS4 and PC. At the moment there is no word on a western version of the demo.