At some point prior to the Lighthouse War, Seymour joined and served in the Erusean Air Force. At the onset of the war, he was tasked with guarding Mihaly A. Shilage on his combat sorties as a member of the Erusean Air Force's Sol Squadron.
On July 12, 2019, Seymour and Wit accompanied Mihaly at Yinshi Valley as he engaged OADF forces in the area. During Mihaly's dogfight with Trigger, him and Wit offered to assist Mihaly but were refused.
On September 19, 2019, Sol Squadron was sent to provide back up for the Erusean Army, which was beginning to falter at Farbanti. Seymour and the Sol Squadron engaged Cyclops and Strider Squadron over Farbanti. During the fight, Sol 1 and the rest of his squadron retreat when the Usean satellite system goes offline.
As various nations in Erusea began declaring their independence, Seymour and the squadron resided in Shilage. On October 24, 2019, they took off from a tunnel to defend Shilage Castle from an attack by Strider Squadron, as Sol 4 and Sol 5 were shot down, Mihaly arrived and dismissed Seymour and Wit.
On October 31, 2019, Seymour and Wit joined the newly-formed Osea-Erusea coalition in an operation to shoot down the Arsenal Bird Justice. They were forced to retreat as the new ADF-11F UAVs had entered the airspace. The following day, they joined the remaining forces to take down the UAVs.
- The Rose Emblem, Ace Combat 7: Skies Unknown.
- "First Contact", Ace Combat 7: Skies Unknown.
- "Battle for Farbanti", Ace Combat 7: Skies Unknown.
- "Lost Kingdom", Ace Combat 7: Skies Unknown.
- "Lighthouse", Ace Combat 7: Skies Unknown.
- "Dark Blue", Ace Combat 7: Skies Unknown.