How about you're a trainer in the Ridanto (or Adorou) region. You're 14 years old and you get to recieve your first Pokemon in Smallwood Village, thrash about 8 Gyms and the Pokeleague, etc., etc. Meanwhile, the evil Team Rodent is looking for world domination. This is the main idea: They want to combine the power of both Giratina and Darkrai to literally make their dreams come true. Therefore they use Darkrai's power to create a dream and Giratina to create a dimension to make it come true.
Do not steal or copy this idea without my permission.