The Promised Day

The Promised Day refers to the coming time of the long-awaited culmination of Father's four-hundred year plan involving Amestris, the Human Sacrifices, the Philosopher's Stone and the Nationwide Transmutation Circle. It was first mentioned by Father during his first appearance in the manga as a toast to his faithful children before he quaffed Greed's Philosopher Stone heart back into himself and has since been mentioned sparingly and with few details. It appears, due to his excitement regarding its proximity, that General Raven and the other members of Military High Command are well aware of the time of The Promised Day, though they may not know all of the true details. From the scattered hints given by those responsible, it would seem that the completion of Sloth's underground tunnel is essential to the Promised Day, but when Alphonse Elric questions Van Hohenheim on what their next move should be regarding the tunnel in Chapter 82, Van responds by telling his son to look not only at the ground, but also at the sky - suggesting that Hohenheim himself knows all the details regarding Father's true plan. In Chapter 83, Ling - knowing the truth from inside Greed's soul - relays to Edward that Father plans to open The Gate when the Promised Day arrives.

Al and Van, knowing the truth, begin a contact chain from Mason to Sig and Izumi Curtis to Major Miles and Captain Buccaneer to General Grumman to 2nd Lt. Rebecca Catalina to Lt. Riza Hawkeye to Jean Havoc to Colonel Mustang, informing them all that the Promised Day - the end of this great battle - will take place in the Spring of 1915. The manga takes a short time skip to Spring 1915, when both sides gather all their resources for the final clash. In Chapter 89, as the final march begins, the younger siblings of Sergeant Denny Brosh declare that there is to be a solar eclipse on that very day, suggesting perhaps (in conjunction with Hohenheim's earlier statement) that the eclipse (and perhaps the celestial circle created by the sun's corona around the moon) is part of the ritual that will open the Gate.

Despite the combined efforts of everyone involved in its prevention, Father's plan progresses with relative smoothness as he summons the four independent Human Sacrifices (Ed, Al, Izumi and Van) and also sacrifices Pride's Philosopher's Stone in create and summon a fifth - Roy Mustang. With the five Human Sacrifices gathered around him at the center, Father enacts the final step of his plan as soon as the solar eclipse reaches its peak.

The Nationwide Transmutation Circle activates in Chapter 104, drawing in the souls of every single human being in Amestris to the center. As the Nationwide Human Transmutation occurs, the individual Gate of each Human Sacrifice is forced open, causing them to conflict with each other. This clash releases enough Human Transmutation energy to open the Gate belonging to the Earth itself. As the massive Gate opens under father's control, Father expands his body to massive size with the energy of the transmutation and activates the circle in the sky created by the sun's corona around the moon which resonated with the circle on Earth to open the Gate of the Heavens, which Father calls "God". The planetary and celestial gates pull against each other and Father pulls the energy of both Gates into himself. As the dust clears, it becomes apparent that all humans within the country save for the Five Sacrifices, Mei Chan and Greed (who both happened to be near the center at the time) have fallen silent and soulless. Father emerges clad in a new, perfect body - resembling Edward and housing the energy of a country and a god.