If you could rewrite the ending to a series...

Season 3.

I would rewrite the end of Friends, and have Courtney Cox and Jeniffer Aniston have great lesbian sex. That would have been amazing. Oh and it would be on HBO so tits and ass could be seen.

I didn't know Friends was produced in Japan... and animated.

This is easy, I would continue Getbackers. The way that show ended is the biggest tragedy in anime history.

That and Kare Kano both deserve continuations.