Instructions: In this task, you're given a story (which contains five sentences only). Your task is to find all the characters which are available in the given story.
Input: Sentence1: Nina caught a turtle at the pond. Sentence2: She brought it home to be her pet turtle. Sentence3: But then her brother taught her about turtles. Sentence4: Nina decided to set her turtle free. Sentence5: She didn't want to be a cruel captor!
Output:
Nina, Brother