A while back I wrote a Star Trek: 2009 fanfic staring a female Kirk, in which the spirit/soul/katra of her Prime self somehow gets stuck inside her head. This leads to many incidents where the elder self helped her younger self with many situations because she’d experienced them before.

When it comes to most time travel stories on here, it’s always mental; the time traveller almost always ends up inside the body of their younger self.

So what if the consciousness of Future Buffy travels back in time - and ends up sharing a body with younger Buffy? 

This would lead to many comedic possibilities, since the older Buffy will find the need to comment on everything that’s happening. But she also becomes a guide of sorts to younger Buffy, helping her with the many choices in her life and making sure she doesn’t make the wrong ones.

If younger Buffy tells anyone about older Buffy, have her tell Giles and Spike.

Have it so this Buffy is from Post-“Chosen”; she loves Spike and thinks he’s dead. Whether or not an older Spike shares a body with his younger self is up to the author. 

Also up to the author how long the story lasts for – one season or multiple seasons?

The story can take place in either season 2, 4 or 5.

Has to end with older Buffy (and older Spike if you do include him) fading away since the future they’re apart of no longer exists, thanks to all the changes that have been made.