Throughout the war, the Seirans were unable to get the people of Orb to support them because most of them were loyal to the Athhas. They reveal themselves as cowards and they wanted only the power, not the responsibilities. After they got killed, Orb got blame because of them. However, with them dead ends the Seiran Family.
Yuna Roma Seiran
Yuna Roma Seiran is the son of Unato Ema Seiran, the prime minister of Orb that succeeded former Chief Representative Uzumi Nara Athha and Representative Homura after their deaths. Yuna is also Cagalli Yula Athha's fiancee by arranged marriage, a union that was approved of by both their parents, a revelation that is revealed by Myrna, Cagalli's caretaker. Yuna is mostly used as comic relief, presented as a villain who sees himself as more calculating and dashing than he actually is.
He is impulsive and controlling. He told Cagalli that neither Athrun Zala nor Kira Yamato could be around them because those two are Coordinators and he and Cagalli are naturals. It would be "unsafe" to have Coordinators around them.
Post Break the World Incident
After the fall of Junius Seven, Yuna aided in his father's decision to have Orb be allied with the Earth Alliance, as it was readily apparent that the Atlantic Federation was adopting a 'you're either with us, or against us' stance. However, Cagalli was strongly against the alliance with the Atlantic Federation because being onboard the Minerva, she realized that they had managed to helped in breaking apart Junius Seven to cause less damage to the Earth. However, Yuna is able to successfully manipulate Cagalli into agreeing with the alliance.
Because of Orb's treaty with the Earth Alliance, the Minerva is forced to depart from Orb. Yuna deploys the Orb forces out to prevent them from reentering their waters just as the Minerva leaves. There is a massive Earth Alliance fleet waiting for the Minerva just outside. (Yuna sold the Minerva out to the Earth Alliance.) However, Shinn Asuka activates his SEED mode for the first time and lays waste to the Earth Alliance forces with his ZGMF-X56S Impulse, forcing them to retreat. Yuna was shocked that the entire fleet was defeated by a single mobile suit.
Soon after, Yuna is about to be married to Cagalli Yula Athha, but right before they can be officially married, Kira Yamato showed up in his ZGMF-X10A Freedom, disabling the Astray mobile suits. Yuna hides behind his wife-to-be, before running off, allowing Kira to successfully retrieve his sister, who nonetheless protested.
Yuna was outraged, and ordered the immediate destruction of the Archangel and Freedom. However, Captain Todaka, in command of the fleet ready to recover Cagalli decided to let the Archangel to escape safely out of his deep respect for its warriors on board, whom fought by his side in the previous war.
Battle of the Dardenelles
During the Battle of Dardanelles, Yuna acts as Supreme Commander of Orb's forces ready to intercept the Minerva. Right before the Minerva fired its main cannon, the Freedom showed up and disabled it. Then Cagalli showed up in her MBF-02 Strike Rouge with her emblem on it and ordered all Orb forces to retreat. However, because Neo Roanoke had convinced him that there would be severe consequences for Orb if they backed out of the fight, Yuna refused to acknowledge that Cagalli was in the Strike Rouge (even though he knew perfectly well that she was), claiming that she was either being brainwashed or was an imposter, and ordered missiles to be fired at her and the Archangel, but Kira jumped in front of Cagalli and destroyed the approaching missiles.
Battle of Crete
In another vain attempt to please the Earth Alliance and make a name for himself, Yuna ordered the Orb fleet to engage the Minerva again at the Battle of Crete. However, this battle goes very badly and ends with the destruction of Orb's flagship Takemikazuchi. Although Captain Todaka does not have a very high opinion or respect for Yuna, he nevertheless urges him to abandon ship, which Yuna does, while Todaka remained on board just as Shinn Asuka delivered the final blow with his Impulse.
ZAFT's invasion of Orb- "Operation Fury"
Later, after Logos is revealed to the world by Gilbert Durandal, Lord Djibril flees to Orb under protection by the Seirans. However, the Seirans deny sheltering Lord Djibril in Orb. Their denial is worthless as ZAFT invades nonetheless. As the battle quickly turned against Orb, Cagalli returned to lead her country's forces. As Yuna was unable to successfully command, he was delighted at Cagalli's return and was easily tricked by her into returning control of Orb to her. Her first command was that Yuna be arrested for treason, an order many officers frustrated with his incompetence happily acknowledged, beating him up before subduing him. Yuna is then confronted by Cagalli, who demands to know where Djibril is. Cagalli punches him for all the lies and for all the people that die because of him. Yuna tells the truth: he doesn't know and that Djibril was at his house before and is nowhere to be found now. Soldiers escort Yuna out afterwards. Yuna is ultimately killed by a falling ZGMF-2000 GOUF Ignited that lands on him when he attempts to flee from his Orb captors. Yuna lost all power to Orb. Cagalli restore Orb as a neutral . Yuna and his father died in vain when Orb became neutral again and Lord Djibril died and Logos lost the war.
Unato Ema Seiran
Unato Ema Seiran is the prime minister of Orb and a member of the high ranking Seiran family. He is also the father of Yuna Roma Seiran and had a hand in the arranged marriage between his son and Cagalli.
After the Junius Seven incident Unato felt the need to join up with the Earth Alliance but received strong opposition from Cagalli. With his political experience and high status Unato was able to also manipulate the young and inexperienced leader to the degree where she finally agreed with his idea.
When Lord Djibril had to flee Heaven's Base after ZAFT overtook it he went to Orb where Unato and Yuna allowed him to stay. When ZAFT requested for Orb to hand Djibril over the two Seiran's denied that he was even there which resulted in ZAFT attacking Orb. During the battle Unato takes safe haven in a shelter along with other Orb officials but that place would turn out to be his grave site as a ZAFT mobile suit crashed into the shelter killing him amongst others. In the manga, Djibril kills Unato.