I'm with Marvel and Kaibasgirl on continuing it, Firefly.
I highly doubt Aang wouldn't save her.
Too sweet of his character to not save his friend. Otherwise I'd be wondering who needs enemies these days....
Aang would attempt to rescue Toph from the Spirit World.
No doubt about that.
He's the only one who can anyway.
The keyword here is attempt. Once we add the 'K' factor things might be different.
Aang would learn what it really is like to be a hero. He'll learn that being a hero isn't all sunshine and fruitpies. Yes, he's been roughed up, shot at and struck by lightning but he's never been forced to make a choice.
The chakra sessions with Pathik don't count. Pathik never forced Aang to do anything. He only gave guidance and advice.
With Koh or any other major threat, Aang might just realise that hero's bleed in more ways than one.
That a hero's life...is sacrifice.
Koh: "The water bender is badly hurt...she might not make it."
Aang: "Sokka and Zuko are still with her. They'll save her."
Koh: "Yes...they might. But they might fail too. Neither of them are healers and the wounds do look oh so terrible. I can save her. You know I can."
Aang: "....."
Koh: "Just let me have the blind girl and your beloved can live."
Aang: "....."
Koh: "I understand if you need time to consider my generous offer. But do hurry...the sands of time only fall one way."
Aang: "....."
Koh: "The earthbender has served her purpose. You've mastered earthbending. You have no further need for her. But the water bender....so loving, so gentle. She fills your heart up in such a way you'd die for her wouldn't you? That is what you said...you'd defeat Ozai and save the world...all for her."
Aang: "....."
Koh: "Give me Bei Fong's soul and your water bender may live. You will be her savior. You will redeem Kuruk's folly. he couldn't save his beloved Water Tribe maiden...but you can. And the water bender will love you for it. I'll tell her you saved her."
Aang: ".....Zuko and Sokka will save Katara..."
Koh: "And say HE does. Your beloved will fall into the arms of the traitor prince. Not yours. And that will be yet another loved one the Fire Nation has taken from you. I can make it so that she never leaves you. All I ask in return is...well, do I need to repeat myself?"
Aang: "...I will save her..."
Koh: "Just let me have the earthbender. Her destiny has been fufilled. Her mortal life has been one of neglect and lovelessness. Why subject her to such an ordeal by bringing her back? Your comrades will understand. The water bender would be most grateful, I'm sure. Katara has so much to live for, her brother, her father...YOU. Are you going to take all that away from her by not giving me the chance to save her? Time grows short."
Aang: "....I..."
Koh: "Do the right thing Avatar Aang. Do it for your beloved."
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What we'd like to see is of course Aang saving Toph and that it turns out Sokka and Zuko were able to get Katara medical help just in the nick of time.
If he choses the alternative.....
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Aang: "KOH!"
Koh: "Yesss? My, my...it must be taxing trying to contain all that rage behind such a dead face. You should smile more....like your earthbending teacher here."
Aang: "You lied to me."
Koh: "I did? You'd think I'd remember lying to the almighty Avatar."
Aang: "Katara's...gone."
Koh: "Careful. No crying now. You know what happens if you cry."
Aang: "She left."
Koh: "Did she now? She's passed on has she? I don't recall seeing any new faces."
Aang: "She left me. They all left me."
Koh: "Oh yes, I remember now...the prince was able to save her life. I owe Roku a pat on the back for having such a noble decendant. Saved me the trouble of healing her myself...not that I would have. I said I COULD save her not that I WOULD."
Aang: "She said she hated me....she called me a selfish brat...she called me a monster."
Koh: "Aren't we all?"
Aang: "Why? Why are you doing this to me?"
Koh: "The question is: 'How could I NOT?' You pathetic little whelp. What I did to Kuruk was punishment. For you...it was a test. Of your resolve, your commitment, of your heart."
Aang: "Then why did you take Toph? Why did she have to suffer?"
Koh: "Silly boy. You know nothing about the truth of the Halls of the Faceless. I spared her. I spared her from you. Same as I did with Kuruk's Ummi."
Aang: "Why not punish me directly?"
Koh: "What you are experiencing now...the pain, the loneliness, the sheer gravity of your foolish mistake...the searing of one's own soul by guilt, regret and remorse...no, I could never hope to inflict such a delicious pain as that."
Aang: "I hate you."
Koh: "And with such a straight face....bravo, BOY. Just what do you hope to accomplish here? Hmmm? Force me to return the earthbender to you? Is that it? Are you going to summon the full power of the Avatar Spirit upon me?"
Aang: "....I...I...can't...."
Koh: "I didn't think so. It is the Avatar Spirit that empowers you. Your soul is seperate from it. Charged with safe guarding the world, the Avatar Spirit never leaves the mortal plane, it simply moves from host to host. Which is why you and all those before you have no power in the Spirit World. Here...you're just like any other lost soul."
Aang: "No...nonononono..Forgive me...Toph...I'm sorry."
Koh: "Tears? Emotion? In front of ME? Are you daft, boy?"
Aang: "Take my face, Koh. Please."
Koh: "No."
Aang: "Why?! Why not?! You'd take the face of a blind girl but not mine?!"
Koh: "Oh believe me, as exquisite as your emotions are, I cannot take your face. You are the Avatar. The mortal realm needs you. Killing yourself wouldn't do much good either, I still won't take your face. I will not give you the privilege of entering the Halls of the Faceless. You will face your sins in the afterlife...just like those before you."
Aang: "What?"
Koh: "Roku, Kyoshi, Kuruk, Yang Chen. They're all still here because of the sins they commited. Sins of Ignorance and Arrogance. And you were supposed to redeem them all, now you're going to end up joining them. If you've quite finished mewling...leave my domain. Immediately. The world needs it's Avatar...such as it is."
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A slight twist on Koh. Each spirit seems to have a role to play. Perhaps Koh's a sort of gatekeeper to the nice part of the afterlife for humans.
Animal based spirits and those of nature, like Yue don't reside there as they are needed outside to run the world.
The seemingly horrific method of gaining entry to that part, the face stealing, might be some sort of test to get in.
The club might be a high class joint but the bouncer's a real piece of work.
That or Koh's still messing with Aang.
That would make him a demon instead of a spirit.