Although Olivia is not a malicious character, she functions as the antagonist because she prevents Viola from getting what she wants. On one hand, the antagonism functions as a fairly conventional romantic rivalry, wherein Viola loves Orsino, but Orsino loves Olivia instead. It would be hard for Viola to pursue a relationship with Orsino because of her disguise, but his passion for another woman makes the situation even more painful, since Viola has to listen to him profess his love for Olivia and even go woo Olivia on his behalf. Olivia further thwarts Viola’s desire to be with Orsino when she falls in love with Viola herself. Viola now has to deter Olivia’s affection while still being considerate of her feelings. The antagonistic relationship between Olivia and Viola is particularly interesting because Viola likes Olivia, and does not want her to be unhappy. In fact, Viola and Olivia are parallel characters as women who are both experiencing unrequited love.
Olivia is not purposefully trying to come between Viola and her desires. However, Olivia’s refusal to listen to Viola or take no for an answer increases the conflict. Olivia persists in pursuing Viola despite being told that Viola will never return her feelings. Olivia was frustrated by Orsino’s insistence on wooing her even after she had rejected him, but she goes on to behave the same way with Viola. Olivia’s behavior remains consistent throughout the play, including when she rushes into a marriage with Sebastian after mistaking him for Cesario. Once she sees the object of her affection reciprocating her feelings, she wants to secure a commitment as soon as possible. Because Olivia is not malicious, her actions as antagonist do not end up causing any actual harm, and in the end, Viola achieves her desire while Olivia finds her own happy match with Sebastian. When Olivia happily tells Viola “A sister! You are she” (5.1.), the antagonistic relationship between the two women has been resolved, and they recognize the way in which they have both wanted the same things all along.