In some Japanese merchandise and other products, Yuna's name may be romanized as Jona Roma Saran.
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 knew that they had 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 because there is a massive Earth Alliance fleet waiting for them just outside. 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 are officially married, Kira Yamato showed up in his ZGMF-X10A Freedom, disabling the Murasame 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 capture of the Archangel and Freedom. However, Captain Todaka, in command of the fleet ready to recover Cagalli decided to allow the Archangel to escape safely out of his deep respect for its warriors on board, whom fought by his side in the previous war.
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 ZGMF-X10A 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 of Neo Roanoke convincing 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 an impostor or she was being brainwashed, and ordered missiles to be fired at her and the Archangel, but Kira jumped in front of Cagalli and destroyed the approaching missiles.
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 culminates in the destruction of Orb's flagship Takemikazuchi. Although Captain Todaka does not have a very high opinion of 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.
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 all for naught 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 ultimately killed by a falling ZGMF-2000 GOUF Ignited that lands on him when he attempts to flee from his Orb captors.