Ryoma is not beautiful in the typical sense of the word.
Before he met the eldest prince of Hoshido, Xander used to believe beauty meant something else entirely. When he thought of the word, he imagined graceful women with curled hair and floor-length silk dresses twirling across the ballroom, faces adorned with makeup and perfume. His sisters, Camilla and Elise, were beautiful. It was a term he had applied solely to women; it seemed only natural, after all, to equate beauty with the most aesthetically perfect.
Ryoma is different. Xander had been unwilling to admit this at first, but through their countless clashes in battle, he found himself captivated by the other man's skill and ability. Ryoma's beauty is in his elegant movements on the battlefield, the way he swings his blade with such ease and fluidity. It is in his undying will, his unwavering courage, and his loyalty toward his homeland. It shows in his actions, his self-sacrificial love toward his family and his comrades.
Though the two might have been from different kingdoms, Xander cannot help but admire Ryoma from afar (and if he is honest to himself, his feelings go far deeper than mere respect. Ryoma is the man he had always desired to become ever since he was young, and a more noble prince than he could ever hope to be. Xander cannot bring himself to envy the other man, though, so he simply watches him from a distance).
When the war is over and peace returns to the land, they are now the kings of their respective homelands. Ryoma invites Xander and his family to the Hoshidan palace for a visit intended to bring friendship between the two kingdoms, and he accepts the offer. Xander had never wanted bloodshed, and now he hopes that the two kingdoms can establish a long-lasting peace.
After dinner, the two are strolling along in the palace gardens, chatting about the state of affairs. Xander cannot help but admire the gentle atmosphere of the place; though dusk is quickly falling, the tranquil sounds of nature fill the air, birds chirping and water rippling. Ryoma looks so peaceful, so at home among nature, Xander observes. He walks calmly and regally, his hair and robes ruffling in the gentle spring breeze. It as almost as if he has been captured in a painting, surrounded by scattering cherry blossoms and framed by the peaceful beauty of the landscape behind him. Xander cannot help but smile as he gazes at Ryoma, and suddenly it occurs to him that this scene constitutes the true definition of beauty.
Ryoma meets his smile with one of his own, soft and gentle. It is a far cry from the murderous looks they had previously exchanged on the battlefield, and that knowledge alone gives Xander hope. Hope for the future of their kingdoms, and perhaps for the future of their relationship.
"Let us return to the palace," the other man is saying. "It is getting late."
Xander nods in agreement and begins to follow Ryoma down the path leading back to the palace, back to where the others are waiting. He walks with his hands behind his back, admiring the serene beauty of his surroundings.
Spring is the season of birth and renewal, after all, and Xander is surprised to find himself hoping that someday he and Ryoma can become something more.