Summons are a major part of Final Fantasy. They're embedded in the games' lore and mechanics—and in Final Fantasy 7's case, they doubled as a showcase for the PlayStation's cool graphical effects. Unsurprisingly, Summons are back in Final Fantasy 7 Remake, but they work quite differently from the original game.
Earlier today, the official Final Fantasy 7 Remake Twitter account posted a video wherein the game's producer, Yoshinori Kitase, explains how Summons happen in Remake. After equipping Summon Materia, you can call Eidolons onto the field during boss battles and certain fights that meet "special conditions." They fight alongside you automatically for a set time while you continue to control the rest of the party. Once your ATB gauge fills up, you can select one of the Eidolon's abilities from the ATB menu and perform a powerful attack.
Note that Kitase explains the system using Ifrit as an example; the specifics of summoning might change from Eidolon to Eidolon, but the gist seems to be you equip Summon Materia, it resonates when you fight a boss or special monsters, and then the summoned monster fights with you until you can select its specific attack via the ATB menu.
There's no doubt that some fans are going to be disappointed to learn you can't summon Bahamut Zero on a whim to nuke a party of bandits from orbit like you can in the original game. This "new" system sounds quite similar to Final Fantasy 12's method of summoning, which I personally find underwhelming. Well, as much as I appreciate how straightforward summoning is in Final Fantasy 7 vanilla, I can't wait to call Knights of the Round onto the field and watch my PlayStation 4 melt down when twelve giant knights fly to my side.
The first part of the Final Fantasy 7 Remake is coming in March 2020. Prepare yourself by checking out our Final Fantasy 7 Remake guides.