Sit is one of four actions that a player can acquire throughout the game. Sit is used outside of battle to restore both health and mana points to all members of a player's party. When not in combat, sit can be used by pressing the x key, or alternatively, accessed via the action window (My Info > Expression > Action).
Unlike some other actions, the level of sit cannot be increased. The amount of health and mana restored by sit scales with a player's level thus allowing high level players to still gain benefit from using sit without having to spend long periods of time sitting to fully recover.
Although available for sale at a fixed price of 500 gold from the market, this action can also be easily obtained for free by completing the Special Signs quest from Amane, available early in the game in the Forest of Spirits dungeon.