Nintendo just released a new trailer featuring heroes from the upcoming game, Fire Emblem Heroes, entering Fire Emblem Heroes. Hilda, Hubert, Mercedes and Petra will be summonable in the summoning event. The event starts on August 7th till August 28th.
A new story chapter unveils as the summoning event starts. The chapter will be featuring the new heroes, Thrasir and Alfonse. After the event ends, you can get the new heroes in the future summoning events.