Complex sentence: Nicknamed, she is an eccentric but friendly and outgoing girl, with a mischievous yet good-natured sense of humor and is the leader of the "Lucky Star" crew, and the protagonist.
Split into simpler sentences: Nicknamed, she is an eccentric but friendly and outgoing girl, with a mischievous yet good-natured sense of humor. She is the leader of the "Lucky Star" crew, and is the protagonist.