As of today, players of Tokyo RPG Factory and Square Enix's I Am Setsuna can download the Temporal Battle Arena as a free DLC exclusively for Nintendo Switch. Sorry PS4, Vita, and PC players, the battle arena is for the Switch version of the game only.
The Temporal Battle Arena introduces a new way to play against friends in turn-based battles. It will enable players to upload and download parties for battle, allowing them to create their perfect character set-up for battle against random parties of various skill levels, or to battle against a friend's party data by entering their player ID.
There is no matchmaking for the Temporal Battle Arena, so you won't be up against random players, you'll need to have their player ID.
To access the arena, Nintendo Switch players will need to download the latest patch and have completed the game. Then, they can revisit the Frozen Lands and gain access to the Arena after encountering a character named "Togi".
If you haven't picked up I Am Setsuna, this game mode probably won't entice you, but maybe it's classic JRPG feel will?