Immortals 
Huge thanks to nikkeh09 for drawing the scan for me! ^^
Also, I'm going to do a short explanation and a long explanation. The long one will include an in-depth analysis of the song and how it applies to Jack x Wuya (from Jack's POV), and the short one will be for those who are too lazy to read the long one.
Short Analysis:
"Immortals" by Fall Out Boy represents Jack x Wuya because it details Jack's love for Wuya, as well as his understanding of his own weakness compared to Wuya, and his desire to put away the idea of who is more powerful in order to be able to love and be loved unconditionally by Wuya.
Long Analysis:
Before I talk about the lyrics, let me talk about the style of the song. While Jack Spicer seems to be the type to listen to hard rock, rather than pop rock, the energy, almost anger, would perfectly fit his attitude towards Wuya, and its stylish feel makes it seem more like something he would listen to.
They say we are what we are
But we don't have to be
Jack is a whiny, weak wannabe villain. Wuya is an all-powerful, immortal witch. That's what they are. And because that's what they are, they shouldn't fall in love. But that's not how it has to be.
I'm bad behavior but I do it in the best way
Despite his claims to being "evil", Jack Spicer has barely gotten past "bad behavior," but he's getting close, all while doing it in his own stylish way, thus making it the "best way".
I'll be the watcher of the eternal flame
I'll be the guard dog of all your fever dreams
When Wuya was in her ghostly form, she was nearly powerless, so she had to rely on Jack. Even if she's not still in her ghost form, he's saying that he is still willing to work solely for her.
I am the sand in the bottom half of the hourglass
Despite all his weaknesses, Jack Spicer is actually quite powerful. The best example is in the episode "Time After Time Part 1", where it is shown that in a world without Omi, and evil prevails, it is Jack Spicer who becomes the ultimate evil using he mecha he creates. He manages to capture all the other, "more powerful" villains and hold them prisoner, including Wuya. This especially ties back into the idea of an hourglass because it shows that it's only a matter of time before he becomes the most powerful one.
I try to picture me without you but I can't
Whenever Jack Spicer tries to leave Wuya and work with some other partner, he ultimately fails at everything he does. It's only with Wuya that he has any success - making her the only one he can "picture him with".
'Cause we could be immortals
Just not for long
Jack Spicer is a mortal villain compared to Wuya, who is immortal, but he is begging her to forget that, and consider him to be immortal, too, even if his eventual death will cut that belief short, making "us" immortals, but "not for long."
And live with me forever now
Pull the blackout curtains down
Jack wishes she would ignore the battle, against good, "pull the blackout curtains down", and reduce her world to only include her and Jack, and live with him "forever", in the belief that he, like her, is immortal.
Sometimes the only pay off for having any faith
Is when it's tested again and again everyday
Many times Wuya has betrayed Jack's trust, thus trusting his faith in her "again and again everyday", but the payoff comes when she ultimately comes back to him, because he is the only one who sees things the exact way she does.
I'm still comparing your past to my future
Wuya's "past" is that she used to be (well, still is) an all-powerful, immortal witch. He's considering her past and how it may apply his future, and the possibility of actually becoming immortal, even if that is impossible.
It might be your wound but they're my sutures
In her past Wuya was defeated, and because she was defeated, it means she's not invincible. While she may not like to face her defeat, the fact that she's not infallible gives Jack Spicer hope that she may overlook his own mistakes.
And then the rest of the lyrics just repeat.
Anyway, that's... a really long description, but I hope I got my thoughts down on paper (er, computer) well enough for it to make sense ^^'
Basically, my point is that every single lyric to Immortals could apply to JackXWuya in some manner.
I hope you like the wallpaper and reading the description, even if you only read the short analysis. ^^
