What Kin?
Cesario is accused of slashing both Sir Andrew and Sir Toby, which she did not do. Ironically, her long lost twin brother did the act and admits to it as he comes into the scene. The twins both look the same and have been confused for one another.
The Duke
Cesario has entered the service of Duke Orsino as a man. Ironically, Cesario is in fact, Viola and the Duke proposes marriage to Viola once he realizes she is a woman.
Olivia
Duke Orsino uses Cesario to constantly profess his love to Olivia. Ironically, Olivia wants nothing to do with the Duke, and the Duke eventually is engaged to Viola.
Love
Malvolio is made to believe that Olivia is in love with him. Ironically, it is a plot preyed upon Malvolio which ends him up in captivity and torment for most of the play.
Antonio
Antonio is a sea captain who knows the dangers of the sea. Ironically, he enters into the stormy sea in order to save Sebastian as he has great affection for the young man.