Who cares if it's a little predictable and is seen as cliche now? Hiro going up to spend the rest of his life with Lucia, surrendering the right to return to Lunar in the process, melted your heartstrings. Especially Lucia's reaction. Admit it.Even cliches are good when done right.
Lucia's theme, the song that plays during that moment, is also very heartwarming.
In Eternal Blue, after Lemina is thwarted by the rest of the party in her attempt to charge the inhabitants of the snowbound village for getting rid of the monster, if you talk to the sick young child in the village, you'll see the following dialogue (except in the remake), which doesn't quite square with her established personality:
Lemina: Somehow, that "thank you" makes it all worthwhile.
Hiro and company giving Ghaleon a Patrick Stewart Speech, declaring that they'll beat Zophar with the "power of humanity".
Lemina's speech when she confronts Borgan in Neo-Vane.
"We must hold together!" - Note the distinct difference in Lucia's behavior before and after the party goes to fight the monster creating the snowstorm. After Lucia rejoins the party, she gains access to her Healing magic. If the entire party has taken damage, she has a priority system which tells her AI who to target first. One guess as to who is at the top of the list, and here is a hint - his name starts with "Hiro".
In-universe, it's a massive source of trauma for Lucia, but for the audience, Luna's recorded message in the remake is this, spoken with a motherly sweetness that shows that she knows how shocking her absence from the world is for Lucia.
Luna: Lucia, the goddess Althena does not exist any longer in this world. Let me explain so that you will understand. My task as Althena was to lead the humans and control the power of the Silver Star so that one day, when the Blue Star was reborn, the humans could return and we could begin anew. However, Lucia, I came to know that while I existed, the humans were not truly happy; they lacked a sense of self-reliance, a sense of pride in their accomplishments. They had become too dependent on me. When I last came to this world in human form, something quite marvelous happened. I returned to this world as I had many times previously; however, this time, I was born into the form of a girl named Luna. As Luna, I grew and fell in love with a Dragonmaster named Alex. It was to be my final rebirth. You see, I chose to remain a human, surrendering my immortality for love. And now, Lucia, you have come seeking my aid... and yet, I no longer exist. But what you must know is that you hold the power to accomplish your mission — it has been near you since you arrived. Humans possess the remarkable ability to rise up in adversity and overcome obstacles to make the future bright for their offspring. Lucia, you have never been alone in this journey. To reach this tower, I know that you must have had the help of many good friends. If you trust what you felt in this journey, and also in the power of the companions who've stood at your side, then, you need only to believe in the power of humanity to gain it. If that power becomes yours, you shall achieve the one thing Zophar fears most: victory.