Elfaria had witnessed that scene because of her own mistake. She had forgotten the seeds of the tea tree on the table onboard the Cradle. She turned around right away, but her playfulness got the better of her, so she decided to sneak up on the two so she could surprise them.
“... Reios-sama... can you...”
However, just before she was about to jump out, she overheard Koutarou and Clan's conversation. As a result, she understood that now wasn't the time for something like that.
“... only live the fate given to you as well...?”
Elfaria was the crown princess. At this rate, she would eventually bear the fate of becoming the empress. However, she wasn't satisfied with that fate. She wanted to live freely rather than travel down the path laid down for her. That was one of the reasons for why she had devoted herself to her research. When Koutarou had appeared before her, she had hoped that he would be the one to free her from her path.
“... Reios-sama...”
Yet, that Koutarou was yet another one troubled by the path laid down before him. You could say that Elfaria's hopes had been off. She felt disappointed. However at the same time, there was an emotion budding within her. That was sympathy for the suffering Koutarou, and a sense of yearning born from that sympathy.