While there isn't a specific gameplay mechanic officially named "Solid Feature," the phrase likely refers to a "solid" or major gameplay addition introduced in this installment. The most prominent new features in Disgaea 6 include:
The text you've provided appears to be a partial reference to the for the Nintendo Switch version of Disgaea 6: Defiance of Destiny . The full Title ID for the standard US/EU release of the game is 0100ABC013136000 .
New automation tools that work alongside D.I. to allow for high-speed, hands-off grinding.
A utility at your base that lets you share experience, Mana, and stat-boosting extracts with party members who weren't in the active battle.