The Grand Hero Battle starts on February 10th and runs through the 14th. As shown in the silhouette, we will likely be able to recruit Narcian from Binding Blade during this event.
The Japanese Tweet states that he will have a 3★ rating, so this will be the first chance you have to gain a 3★ hero without paying orbs.
Update: As suspected, the character obtained from the first Grand Hero Battle is indeed Narcian.
Compared to regular Hero Battles, Grand Hero Battles are extremely challenging. The Normal map (which awards 2★ Narcian) has a recommended Level of 25, while the Hard variant (which awards 3★ Narcian) suggests 35.
Like other Hero Battles, if any of your allies fall, you will get a Game Over. On top of this, you cannot continue a failed battle by using a Light’s Blessing or an Orb.