well basically, subspace is the story of why all the playable characters in the game are in the game.
link is travelling through the forest to get master swird when he sees yoshi.
lucas and ness are just rando,ly attacked by porky when ness is turned into a trophy. lucas wants to get revenge
DK and diddy are trying to stop bowser fropm stealing their bananas.
pit is watching the fight between mario and kirby when he sees sonething wrong taking place. he goes to help them.