There are so many different ways you could turn season 6 around. But if you want to approach it froma shipper approach...
B/W
Okay, during bargaining I think we should see Willow bargaining with something. Anything. In the show she killed a deer for her friends return. How about she gives up her wicca powers so Buffy can return. And then Buffy does return, but something is wrong with her. I think Buffy should get Willow's powers, and that she shouldn't understnad that she has them, she just thinks that soemthing is wrong with her. So she retreats into herself leaving Willow without any powers to help out with. And over the summer let's say that Tara left because she couldn't helpWillow's depression (Over Buffy death). Buffy comes back, and OMG everything has changed: Willow has no powers, Dawn is actually compliant, adn another thing XAnder adn Anya got married because Xander finally got his head out of his a$$ and realized how short life is. Okay i went off into a rant, but back to the season. There should be soemthing about how dawn was allowed to stay. Maybe Willow used a spell to be able to keep Dawn. Now Willow has no powers and has been cut off from Buffy, xander and anya are away on a honey mooon, so Willow cuts off her emotions and leaves the house. Let's say she even starts dating guys again.( so there is no emotional connection) and then have Tara come back. So there can be angstyness between Tara and Willow, Buffy/Willow. Tara turns to Buffy for support. I think that during the time that Willow has moved out and started hooking up with guys ( and Xander n'Anya hasve returned) Buffy should relaize that she loves Will. And that's where the singing episode comes in and all the secrets come out. Cept Willow isn't there so she doesn't know about Buffy feelings. Tara and Buffy both love Willow, but niether want to push Willow into a descision. They think that Willow will stop going out with guys if they all sit down and try and work it out, but Willow can;t handle seeing Buffy and runs off before they can tell her anything.
And spike? What Spike? Just kidding. I think that he should go to Warren and get his chip removed since he knowes that warren can do robots. Warren does remove it and say spike snaps that one guys neck ( not Jonathon or warren, but the other one.) so warren or jonathon won't say anything to buffy. Spike has come up with the ultimate plan: Kill/tourtue Willow to get Buffy off her game so he can finally kill her. And now that Willow doesn't have her powers she is defensless. And she has moved out. However Willow has turned into our neighbor hood nasty girl, and when Spike shows up being Mr. Charm ( so he could kidnap her/ and act like he is still chipped) she decides to sleep with Spike. Now don't start throwing things at me yet.
Reasons why Willow would sleep with Spike:
1) Get back @ Tara. I know that sounds mean, but the girl left her alone without any support while Buffy was dead. Besides Willow doesn't care because Buffy doesn't love her.
2) Because Spike showed an intrest. (how is she supposed to know that he wanted to kidnap her?)
Back to the storyline. Spike starts showing up while Buffy patrols telling her about how he is nailing Willow, etc. And Buffy gets mad/sad and won't belive it. (Spike is killing again. He's our big bad. Buffy and the gang, minus Willow, are trying to figure out who is doing all this killing.) Spike sets it up so he and Willow are (for lack of better term) having hot monkey sex in the grave yard, and Buffy sees them. And for the first time in a long time Willow feels something other than depression and guilt when Buffy catches them. She thinks she has lost Buffy forever so she keeps on with her relationship with Spike. Eventually she finds out that he can bite ( maybe he bites her during sex) But she doesn't tell Buffy, she doesn't know if Spike is good or not, but she doesn't really care either. Basically Willow keeps to herself @ school, and doesn't really interact with anyone other than Spike. So Spike keeps running into Buffy during patorls telling her of Willow, and all their sexual exploits, etc. Buffy can't do anything to Spike because Spike keeps saying that Willow loves him. ( Buffy couldn't ever kill anyone she thinks Willow loved) Xander is in denial that WIllow would sleep with Spike. Tara is disheartened. Anya thinks it is weird, and Dawn wants Willow back, no matter what. ( so basically she wants her back with Tara or Buffy, because the gang all know that both of the blondes are in love with Willow)
Anya goes to see Willow, and finds Spike feeding off Willow. Anya runs back to the gang. They are all worried. Spike and Willow saw Anya. Spike decides that the game is up, and kidnaps Willow. The gang shows up and find blood all over, and a note saying that he has taken Will. So the big finale is trying to get Willow back.
Finale:
There should be scenes of all the Scooby's worriedness over Willow. Also the gang puts 2 +2 together and gets Spike, meanign they figure out it has been Spike killing of the inhabitants of Sunnydale. Willow tourtured by Spike until she admits she loves Buffy. Buffy over hears , having already found out ( with the gang's help) where Spike has Willow, but before she can come in Willwo asks why he is torturing her. He tells her to get to Buffy, that it is the best way to hurt her. Willow says why would it matter that Buffy diesn't care about her anymore, and Spike tells her that Buffy loves her. Willow doesn;t believe and Spike points out all the times Buffy has saved her, and how he can sense Buffy's love for her. Then he throws it in her face about how she has been sleeping with him. Buffy steps out at that point. She and Spike fight and as buffy is about to kill him, Spike shouts out that Willow knew. Buffy pauses, and asks 'knew what' Spike takes the oppertunity to change the tables. He gets the upper hand and holds her down, adn tells her..
'She knew that I could bite.' or somethign to that effect. Spike turns her head to face Willow.
'Look at her. She could have saved them if she had just told you. All those lives.'
Willow is horrifeied, coz she didn't know about the killings. And buffy refuses to believe that Willow knew. So Spike drags her over to Willow and shows Buffy Willow's neck. Buffy is shocked .
'She's let me bite her. She tastes so pure, innocent.' Or somethign like that. Spike makes the mistake of lettign go of Buffy while he is talking of WIllow's purity (He's running his hands over her cheek/neck) Buffy stakes him.
Now the season can end on a good note or a bad one.
Bad one: Willow now knowes that Buffy loves her, however, Buffy can't stand that Willow knew Spike could bite, so she doesn't want anything to do with Willow. (that is until the next season, but that is another story)
Happy ending: Buffy takes Willow back. And the finale ends with the repricussions of Willow's actions during the season. AND the whole question of does she choose Buffy oe Tara/
Okay I hope that wasn't to drawn out. I have more ideas , depends on whhich couple you want together.
-Will