The Dream Oath Opera was the famous Opera Scene in Final Fantasy VI. The backstory is that your characters learn that Setzer, the only man in the world with an airship (which, following tradition, you need in order to accomplish anything) is planning on kidnapping Maria, the lovely star at the Opera House. You decide to substitute Celes, one of your party members, for Maria, thus ensuring that you’ll have a chance to speak with Setzer.
The opera itself tells the story of Maria and Draco — who are, of course, lovers — as well as a war between the forces of the West (represented by Draco) and the East (represented by his rival, Prince Ralse). The forces of the West fall, and Maria is taken as a wife by Ralse. She sings the Aria de Mezzo Caraterre (the only interactive part of the opera; the player had to supply the lyrics or else the opera would be ruined):
Oh my hero,
So far away now
Will I ever see your smile?
Love goes away, like night into day.
It’s just a fading dream…
I’m the darkness, you’re the stars.
Our love is brighter than the sun.
For eternity, for me there can be,
Only you, my chosen one…
Must I forget you? Our solemn promise?
Will autumn take the place of spring?
What shall I do? I’m lost without you.
Speak to me once more!
We must part now, my life goes on.
But my heart won't give you up.
'Ere I walk away, let me hear you say
I meant as much to you…
So gently, you touched my heart.
I will be forever yours.
Come what may, I won't age a day,
I'll wait for you, always…
The survivors of the Western army return, Draco challenges Ralse to a duel, and your party accidentally drops onto the stage from the rafters, where they had apprehended Ultros, a recurring miniboss out to ruin the opera. The opera concludes with Setzer descending from the airship and abducting Celes.
The music for the opera was composed by Nobuo Uematsu, one of the huge names in video game composing and the composer for almost every song in Final Fantasy games until his recent break with Square Enix.
The opera plays into the fact that the game is itself operatic — many characters and situations have themes: Celes’ theme comes from the Aria; Ultros’ theme comes from the movement that plays during your fight with him.
At the fourth Orchestral Game Concert, the opera was performed in its entirety by a full orchestra and professional opera singers. It was twenty-three minutes long, and I am to this day still staggered by the depth of effort that went into its execution. Be warned if you try to find it, though: the CDs for Orchestral Game Concerts are notoriously difficult to locate, and (contrary to rumors) the opera is in the original Japanese — not in English or Italian.
Source: http://www.fflyrics.com