Complex sentence: Though he exists in other Reader Rabbit systems, in "Reader Rabbit 2nd Grade", he is the main character, unlike previous franchises in which the story revolved around Reader Rabbit doing various educational activities in which the player would interact to help Reader Rabbit.
Split into simpler sentences: Though he exists in all "Reader Rabbit" systems, he is the main character in "Reader Rabbit 2nd Grade". In the other games, the story revolves around Reader Rabbit doing various educational activities in which the player would interact to help Reader Rabbit.