Lightning – Final Fantasy XIII
Lightning would be an interesting party member if she were in Kingdom Hearts 3; which is likely, considering Square Enix’s undying affection for her and the XIII series with XIII-2 and Lightning Returns.
Contextually, Lightning could play a similar role to Auron in the Hercules world of Kingdom Hearts 2: set in the middle of the events of Lightning Returns, Lightning discovers Sora and the gang, and believes Etro has tasked her with helping them defeat one of the 13 warriors of darkness, but afterwards realizes that she needs to go back to her home world.
If Square Enix were to use her character in XIII, her relationship with Sora would parallel her and Hope’s journey in Final Fantasy XIII – Lightning being reluctant to help him, thinking he is incapable of taking care of himself, but later sees him as a younger brother. She would work perfectly as a party member for Kairi or Aqua if the game is split into three or four character-driven arcs for Sora, Riku, Kairi and Aqua respectively.