As requested by: 
akai_senshi, dusk_eyed, ryoku_chan,odangoatama86. This one focuses on the Zero girls, but there are theme songs for Kio, Soubi, Yuiko and Ritsuka. I apologise that I did not have enough time to come up with songs for all of them. Hope you all enjoy the songs! Also, most songs are in Japanese cause I collect Japanese songs like Whoa!, lyrics translations are provided to songs that I think will be hard to find.
KyouyaXYamato songs:
1. On and On – SnOW (English Version)
I am watching you be I will watch dream
cuz I’m not sure if I will be
forever me, with forever you
Think of the final fight for these two ladies. They’ve agreed, after everything that has happened, to leave the world they knew behind. Kouya loves Yamato for who she is, truly and deeply, and would not have anyone else nor Yamato in any other way.
2. Smile – Full Moon Wo Sagashite:
smile smile
watch me always, watch me forever whenever
smile smile
want to believe, want to feel it forever
smile smile
being able to understand happy mornings and sad nights
I won’t forget to smile
I cannot live without you forever
As long as Yamato, the sacrifice, doesn’t feel pain, neither will Kouya.
3. Itsumo Gawa Ni – Mori
If it is to protect you, then there is nothing to regret
I will take your place in any pain
I will always be near you
Yamato would rather die than to be a burden to Kouya. Add to the fact that Yamato can actually feel pain, and this song becomes even more painful.
4. To be free- Stella Furst (English, from Sol Bianca)
To be free
As free as a bird can be
Got a goal to reach
Be free
As free as a bird can be
Though you may not believe it
They decide to leave Nagisa. Is there anything else to be said?
5. Bokura No Love Style- Hikaru/Kaoru Hitachiin Twins Character Song
chatting with some girl while you’re watching Oh No, No, No
I’m showing off to make you jealous Oh Yes, Yes, Yes
The first time we meet them, Kouya’s jealous. Do we need to say anything more?
6. Tears I cried – Siam Shade
You take the tears I cry and lift me up to the bluer sky
Yes, you gave me hope
Gave meaning to my life, I love you so
7. Melompat Lebih Tinggi (Indonesian) – Sheila On 7 (Translations here)
Together like the forest and the rain
I’m here because you were created
Need I really say more?
Theme Songs!
Ritsuka:
Don’t Dress Me Up- Olivia (Lyrics here)
Why are you being so damn cruel?
Hey look you are a human being like me
Oh, I might trip and fall
But that doesn’t mean I don’t know how to stand tall
I don’t look like her
But I’m glad as hell I am who I am
Ritsuka’s pining for Soubi? Equally this can also be used for Yuiko.
Soubi:
One Winged Angel
Soubi shares some traits with Sephiroth, but most importantly his “burning” desire for Ritsuka, who seems to want nothing to do with him. Then again, perhaps not, no? (You try having friends parody this song as:
He wear lips everyday, he’s so gay,
Sephiroth!)
Kio:
Guilty Beauty Love- Miyano Mamoru (aka Tamaki from Ouran)
My divine punishment is that the love I give will make your heart burst
Nevertheless I am in love with you so I should probably stop this…
Is it Kio’s fault that he’s irresistible? Or so he thinks? XD
YoujiXNatsuo:
Shake Me Down- Siam Shade
Being emotionlessness is good, no need for words, continuing to dance as our feelings tell us
The forbidden moon that won’t tell anyone is intensely coloring our night
‘Nuff said.
Zips: