Complex sentence: He was brought on when Nomura was occupied with other duties including designing the main cast of "Final Fantasy XIII": the main reason for his inclusion was the wish to preserve the game's realism by creating designs influenced by Western fashions.
Split into simpler sentences: He was brought on when Nomura was occupied with other duties including designing the main cast of "Final Fantasy XIII". The main reason for his inclusion was the wish to preserve the game's realism by creating designs influenced by Western fashions.