Aang wanted Katara to be his soulmate.

It made sense. She was the first person he saw after waking up from a hundred year slumber. The first person who believed in him.

She ended up being Zuko's soulmate.

Their bond appeared through writings on skin. Katara had shown him how the scrawls she left on her skin would show up on Zuko like parchment. "This could help us with the invasion!" she had exclaimed, with a smile so hopeful that Aang momentarily forgot his heartbreak.

So when Aang felt tingling on his back, and made sure it wasn't a creepy crawly sent by the Fire Lord in some nefarious scheme, Aang was hopeful. Nervous, but hopeful.

He hoped it was someone he could recognize because he was nervous about fighting the Fire Lord, and very nervous about dying in said fight with the Fire Lord, and very, very nervous about never meeting his soulmate because he died in his fight with the Fire Lord and the only thing she will remember him by is his failure to save the World a second time.

He had explained as much to Sokka, who then took a look at his back, made a pinched face, and said, "Well, you definitely know her and have already met..."

"That's great! Who is she?"

"Uh, maybe it's best if you don't know. You know what, just never look at your back again."

"Is it Suki?"

"Wha-NO! Suki's my girlfriend!"

"Toph?"

"No."

"Katara?"

"Katara's soulmate is Sifu Hotman over there so no-"

"-then who is it Sokka? C'mon just tell me."

Sokka sighs. "Alright, I'll describe your soulmark to you, maybe it's a different person than the one I'm thinking of, but keep in mind that I warned you. Also, just because the universe says this person is your soulmate doesn't mean you have to agree. What does the universe know anyway? It's all the way up there!"

"I'm not going to reject my soulmate Sokka. No matter what."

"No matter what? Are you sure about that? Like 100% super sure?"

"I'm the Avatar. If the universe matches my soul to someone then I trust it."

Aang's soulmark precisely covers the scar on his back. There are light blue, lightning-like, streaks while the heavier scar tissue is covered by a circle of blue flames.

Sometimes Aang questions the universe.