In the beginning

[mooseming]

No: HPFGUIDX 91985

What if the 'other' in 'neither can live whilst the other survives' is
another other?
Oh say the spirit/soul of Salazar Slytherin, which is divided between
Harry and Tom, in effect stopping them from living their own lives.
SS did something very bad back in the beginning, according to the
sorting hat song in OOP more than just the pure blood thing. What if
that very bad thing was messing with old magic and immortality (with
some hideous price to pay). What if the very old magic Lily used to
protect Harry somehow messed with the very old magic SS used to
incorporate his spirit/soul in Tom's body and s/s SS is now in essence
divided?

The final battle then becomes between two mortals, Harry and Tom, for
an immortal soul. If Harry kills Tom perhaps s/s SS will be able to
reconfigure inside Harry and he will be lost unless he can overcome
s/s SS. Maybe Tom and Harry have to join forces to defeat s/s SS?
Perhaps it is in s/s SS interest to kill one of them and he isn't
fussy which 'either must die at the hand of the other'. How can s/s SS
have a hand? What about the hand of destiny in Knockturn Alley or
Wormtail's shiny new silver hand?

OK its all very made up....but it might be right :-)
jo