Portia is a wealthy heiress whose father has died and left her with no other family. Nerissa is Portia's servant, and of a lower social class, but she seems to act more as a sister and friend. Nerissa is Portia's listening ear and empathetic voice. Not only does she bounce Portia's thoughts off of her wisdom, but she also accompanies Portia on all her mental, emotional, and physical adventures. When the audience first sees Nerissa, she is helping Portia categorize all of her suitors to analyze their good qualities, if any. She is also the one who reminds Portia of Bassanio, the one, in her mind, most suited for marrying her mistress.

Nerissa also goes undercover with Portia as a law clerk to assist with Shylock's proceedings against Antonio. Nerissa could have declared Portia a fraud, but she is a loyal friend for life. The two women are so connected, they also play a joke on their husbands together by retaining their wedding rings while in disguise. When the men come home afterwards, they are caught in their faults, which helps to prove the follies of men in their minds and teach the men a lesson. Nerissa and Portia are both forgiving, however, and reveal their parts in the trial and how they set their husbands up for the joke. Therefore, Nerissa is more than a servant for Portia; she is her sister and partner in crime, her loyal assistant and supporter. Anything Portia does, Nerissa also does because of her sisterly love and friendly loyalty.