No, I don't own Yu-Gi-Oh (More's the pity.)
The Oath

Now this is the Law, and all must pay heed
Both Dark and Light and all in between
The dragon and mage, and the fiends with their greed
And such is the Price. It is fair, we deem.

By all the Powers that we hold
By gifts of fearful might
By strength and will that we possess
By Darkness and by Light
We pledge our service to the One
Who summons us from Shade
And binds us to a form of flesh
To do as they have bade.

By Masters Old and Lady Pure
By ancient, nameless Lords,
We pledge our service to the one
Who calls us. With our swords
And powers out of forgotten times
We guard and aid their cause
We do as bid with no complaint
We follow fast their laws

By songs that whisper in the night
And souls that never die,
We never shall betray their cause
And to them, shall not lie
But do our utmost to succeed
To aid their victory
It matters not 'gainst whom we fight
But our success shall be!

If defeat looms, by Power and Pride
We will fight to succeed.
And if we're beaten, bide our time
And take revenge in deed!
By freedom from the endless Night
Our loyalty is assured
We will obey with all out might
And hark to every word.

Our petty feuds we out away
If bid, fight side-by-side
We give our all with no complaint
And patient, we shall bide.
Our gratitude forever runs
Our loyalty is sure
For One who called us from the Realm
Be their hearts stained or pure.

And in return for our great aid
The Masters set us free
From birthing-Realm that reeks of hate
And we their slaves shall be.
For release from the empty wastes
We strive to do our best.
We bow our head before the Lord
And face his every test.

The One who names us gains our trust
Our power at their will
But ask not for a binding call
Hold now, and yet be still.
For power given with True Name
Shall also Masters bind
And tie our sols unbreakable
So choose the proper kind!

The only way to break the Seal
A challenge must be fought
By two who would a one possess
And hold all they have wrought.
If we so choose, the new Master
May free us of the First
And we will sing a joyful song
Free of Master Accursed!

But is we judge the Victor New
As not the Master True
We will be bonded to the One
Who knows what we can do.
For every One of Us who lives
There is a Master Great
A One who knows us, understands
A One we cannot hate.

So serve the Masters faithfully
But wait for the True One
Who gives you name, completes your soul
Together, all fights won!
The Shade and Sun walk side-by-side
Our destinies embrace
We stride together on the Path
We stare them in the face.

Now this is the Law, and all must pay heed
Both Dark and Light and all in between
The dragon and mage, all fiends with their greed
And such is the price. It is fair, we deem.