Aquila is a character from Shin Megami Tensei IV.
As Flynn can learn from the monumental inscription on the obelisk in Mikado Castle, about 1500 years ago, Aquila was the soldier who used the Demon Summoning Program to repel the intruders from the underworld through Naraku. He was known to be the first Samurai and became the first king of the Eastern Kingdom of Mikado. His statue has been erected in the central plaza of the castle.
Statements from the NPCs throughout Tokyo and Mikado suggest that time in Tokyo flows much slower than in the Kingdom. Twenty years before the game's events, in Tokyo, there was a young man with the Demonica gauntlet called Akira. He hoped to retrieve his older sister, who was taken away from him by the angels. To do this, he climbed to the surface above the ceiling created by Masakado when he was defending Tokyo from the ICBM strike five years before that.
Not long after Akira's journey, the Counter-Demon Force, with Skins being one of the members, followed in Akira's footsteps to ascend to the ceiling, but Akira sided with the angels to fight back the Counter-Demon Force. After his triumph he used the name "Aquila", sealed the entrance of Naraku and positioned Minotaur to guard the door to Tokyo.
In the DLC Clipped Wings 1, it's revealed that Akira was eventually convinced by Mastema to turn against the Archangels. However, he was defeated and killed by them. After finishing both Clipped Wings quests, it's revealed that his favorite demon is the Tyrant Aeshma, whose data is kept with Mastema.
When the Akira of Blasted Tokyo declares that he will rename the city as the "Eastern Kingdom of Mikado" in honor of Flynn's deed, Jonathan is confounded after he suggests that Akira would be called the "King Akira of the Eastern Kingdom of Mikado". Likewise, the Akira of Infernal Tokyo is crowned King of Tokyo upon Kenji's death.
The implications are that Aquila and Akira are the same person. Their names are similar with only the ュ in Aquila's name being the difference, which fits the theme of the names of Mikado's provinces being bastardizations of Tokyo regions and areas. Conntow = Kanto, Shene Duque = Shinjuku, Kiccigiorgi = Kichijoji, etc; as these places were named by Aquila himself after his old home. As of Shin Megami Tensei IV Apocalypse, Akira and Aquila being one and the same is confirmed.
- Aquila's name might be a reference to the 1985 movie Ladyhawke, as the movie takes place in the French region of Aquila. Likewise, Navarre and Isabeau are named after Étienne Navarre and Isabeau d'Anjou, two of the characters from said film.