Long ago, there are two alicorn sisters that rule the kingdom. The younger one lowers the sun to make the way for the moon, and the older one rises the moon at dusk. Soon, the younger one noticed that the ponies don't like her day... She became jealous and resentful, and vowed to shroud the world in eternal daylight.

When the older one noticed, she tried to reason with the younger one, but the younger one refused and transformed into a mare of evil light- Solar Flare! The older one gathers the most powerful weapons known to ponykind- the Elements of Harmony! The older one reluctanctly banished Solar Flare and imprisoned her in the sun permanently. Now, she takes responsibility for both day and night.

One evening, Princess Luna lowers the sun after banishing her sister. She decides to sing a song to her sister, who is currently imprisoned in the sun because of Celestia's transformation into Solar Flare.

---

Fate has been cruel and order unkind

How can I have sent you away?

The blame was my own; the punishment, yours

The harmony's silent today ...

But, into the stillness, I'll bring you a song

And I will your company keep

Till your tired eyes and my lullabies

Have carried you softly to sleep

Once did a pony who shone like the moon

Look out on her kingdom and sigh

She smiled and said, "Surely, there is no pony

So lovely and so well beloved as I"

So great was her reign and so brilliant her glory

That long was the shadow she cast

Which fell dark upon the young sister she loved

And grew only darker as days and nights passed

Lullay sun princess, goodnight sister mine

And rest now in sunlight's embrace

Bear up my lullaby, winds of the earth

Through cloud, and through sky, and through space

Carry the light and the warmth of day

And carry my sorrow in kind

Tia, you're loved so much more than you know

Forgive me for being so blind

Soon did that pony take notice that others

Did not give her sister her due

And neither had she loved her as she deserved

She watched as her sister's unhappiness grew

But such is the way of the limelight, it sweetly

Takes hold of the mind of its host

And that foolish pony did nothing to stop

The destruction of one who had needed her most

Lullay sun princess, goodnight sister mine

And rest now in sunlight's embrace

Bear up my lullaby, winds of the earth

Through cloud, and through sky, and through space

Carry the light and the warmth of day

And carry my sorrow in kind

Tia, you're loved so much more than you know

May troubles be far from your mind

And forgive me for being so blind

The years now before us

Fearful and unknown

I never imagined

I'd face them on my own

May these thousand winters

Swiftly pass, I pray

I love you; I miss you

All these miles away

May all your dreams be sweet tonight

Safe upon your bed of sunlight

And know not of sadness, pain, or care

And when I dream, I'll fly away and meet you there

Sleep...

Princess Celestia, still a bit corrupted, decides that her choice has somehow hurt the ponies of Equestria. She thought it foolish to reject her sister's words when she should have listened... She would come back as Solar Flare, for sure.

---

How my deeds pain me as time stretches long

How could I have hurt them this way?

So rest easy now, my punishment's mine

The weight of my crimes are my own

But into that stillness you brought me your song

With your voice my company kept

For your tired eyes and sweet lullabies

In exile I pay you my debt

Once did a pony who gleamed like the sun

Look out on her kingdom and sigh

Dejected she cried, "Surely there is no pony

"Who loves me, or finds any love in my day."

So great was her pain, she rose in rebellion

Against those who cared for her most

She let the dark flame fall on those she ruled

And threatened to grip them in permanent heat

Lullay, dear Luna, good night sister mine

Rest now in moonlight's embrace

May this warm lullaby reach you in dreams

And ease you your passage of days

May my apologies find you this eve

And may my sorrow in kind

Luna, you loved me much more than I knew

Forgive me for being so blind

Soon did her sister do what was demanded

And gave to the Sunlight her due

Breaking the Harmony, she saved her ponies

And banished her, as a wise ruler must do

Such is the weight of the crown that we wear, sister,

Duties we always uphold;

May you forgive me that foolishness mine

And live on with no burden upon your soul

Lullay, dear Luna, good night sister mine

Rest now in moonlight's embrace

May this warm lullaby reach you in dreams

And ease you your passage of days

May my apologies find you this eve

And may my sorrow in kind

Luna, you loved me much more than I knew

May troubles be far from your mind

And forgive me for being so blind

The space now before us, empty and forlorn

I never imagined we'd face them all alone

May these moonless seasons swiftly pass, I pray

I love you, I miss you, all these miles away

May all your dreams be sweet tonight

Safe upon that bed above the stars

And know not of heartache, fear, nor gloom

And when I dream, I'll fly away to meet you soon

Sleep, sleep

Sleep…