Sebastian, though a seldom seen character is an important one in Twelfth Night to the Shakespearean theme of the heroine as the hero. This theme also appears in Much Ado About Nothing and As You Like It in the characters of Hero and Rosalind, respectively. One of the premises of the theme, one which is significant in Twelfth Night, is that typically female character traits when evident in males characters are identified by different terminology. For example, Viola is loyal and devoted as Viola but is persistent and determined as Cesario: Viola's character traits don't change but the label and perception of the trait do change. This can be seen by Olivia's reaction to Cesario/Viola, who appears to be persistent and determined, when in fact Viola is being loyal and devoted to the request of the man she has fallen instantly in love with, that being Orsino.
Sebastian is important to this thematic element because his character traits are identical to Viola's. He is gentle, understanding, loyal, compassionate, intelligent, resourceful, loving. These traits are evident from the nature of his conversations with Antonio. For instance, when Antonio tells Sebastian that because of past indiscretions he is not safe on the streets of Ilyria, Sebastian's only response is that then Antonio must stay out of sight. Sebastian is understanding of Antonio's predicament. In an earlier instance, Antonio overrides Sebastian's decision to go his own way because the Fates are against him. Antonio chooses to accompany Sebastian. From kindness Sebastian is reluctant to share his ill fate.