Following a post about Owain and princehood, I noticed that Lucina is consistently referred to as a Princess, even in the future where Emmeryn, Chrom, Lissa, Chrom’s wife, and Lissa’s husband are presumed dead. That seemed pretty weird to me, so I went and investigated when exactly the royalty of Ylisse become “Exalts” proper.
She seems to only gain Exalt status at the end of The Future Past, after performing the Awakening. From TFP3:
Tiki: Now, Lucina! Your first task as exalt is at hand! Wipe the fell dragon from existence, and usher hope back into the land!
さぁ、行きなさいルキナ…いえ、 Now go, Lucina… no,
希望の未来を統べる、新しき聖王よ！▼ new Exalt, who shall [reign over?] the future of hope!
今のあなたになら… Now, you
邪竜を永遠に葬り去ることができる！▼ can banish the Fell Dragon for eternity!
Until then, she’s a princess.
He takes up the title of Exalt after the end of the game, per his epilogue. (Note that this is NOT immediately after he does the Awakening.) His reason for doing so in the localization is out of respect for the deceased, but in the Japanese there is no reason given in this scene.
And so the war between Ylisse and Plegia was ended. Prince Chrom and Robin worked tirelessly to restore Ylisse’s splendor. This would be no easy task, for the war had taken a heavy toll on the halidom. But with Feroxi muscle and Plegian gold, they brought peace back to the people. All the while, the prince forswore the title of exalt, out of respect to his late sister. Even so, his subjects grew eager for their new ruler to take a wife. And in his heart, Chrom had always known who that woman would be. The royal wedding was a joyous occasion, attended by thousands from near and far. Finally, it seemed that the last lingering wounds of Ylisse’s history had healed. But then, two years later…
戦争は幕を閉じた。▼ And so, the curtain fell upon the Ylisse-Plegian War.
戦後すぐ、クロム王子は○○(告白イベントの相手の名前)と共に Immediately after the war, Prince Chrom, with [name of the partner in the confession event],
イーリスの復興に尽力することとなる。▼ turned to efforts to rebuild Ylisse.
祖国が受けた傷跡は The scars of his homeland
根深いものであったが、▼ were deep, but
ペレジアからの多額の補償と there was a great sum of compensation from Plegia and
フェリアの支援もあって、▼ aid from Ferox;
平和を取り戻しつつあった。▼ Ylisse slowly regained a peace like that of before.
やがてクロム王子は、Eventually Prince Chrom,
周囲の求めもあり▼with demands from around him as well,
婚礼の式を挙げる。▼ held a marriage ceremony with the woman his heart chose.
その日は、On that day,
多くの人々が祝福に湧いた。▼ a great many people gave their blessings.
穏やかで幸せな日々…▼ [They were] quiet days of happiness, as if the scars of battle had healed…
だが、二年後…▼ But two years later…
After Grima’s defeat, Chrom was officially welcomed as Ylisse’s new exalt. His unflinching perseverance through countless hardships made him a beacon of hope for his people.
（新たなる聖王） New Exalt
戦いの後、After the battle,
正式にイーリスの聖王となる。 he officially became Ylisse’s Exalt.
決してあきらめず戦う姿に、In the sight of him facing countless hardships and fighting without [any thought of] surrender,
人々は新たな光を見た。the people saw a new light.
So, I suppose one might speculate that Exalt is a ceremonial title, considering the lack of mass upheaval during the times when there was no formal Exalt, and everyone’s reluctance to adopt the title…