Soulbound

In which the two protagonists are bound together in some psychic/telepathic/empathic/mental/spiritual way.

• Where Your Treasure Is (Harry Potter) by Zeegrindylows
  SS/HG. Post-Deathly Hallows. Severus Snape survives, only to find himself entangled in an enchantment he never expected.
• It's Elemental My Dear Snape (Harry Potter) by Cathedral Carver
  Everything has been figured out, except how to live. Pay attention -- there's a test later.