The second act begins on the seacoast of Illyria. Viola's twin brother, Sebastian, was not drowned after all. He survived the shipwreck and enters on stage talking with Antonio, a sea captain (not the same sea captain who managed to reach shore with Viola). Sebastian, like his sister Viola, is deeply grieved; he is sure that Viola was lost at sea and perished in the storm. He blames the stars and "the malignancy of [his] fate" for his dark mood and his misfortune. He turns to the sea captain, and, feeling that he can be straightforward with him because of what they have both just experienced, he tells the captain that he wants to be alone. He needs solitude because of his terrible grief; his troubles are many, and he fears that they will spread like an illness and "distemper" the sea captain's mood. He cares too much for the captain to unburden his woes on him.
Antonio, however, will not leave Sebastian; his friendship for the young man is strong enough to withstand Sebastian's emotionalism. Sebastian's composure suddenly breaks, and he bewails his lot; if Antonio had not saved him, he would now be dead at the bottom of the sea, alongside his beloved sister. "If the heavens had been pleased," his fate would have been the same as his sister's. He then recalls his sister's beauty, and he remembers her keen mind, a mind that was extraordinary and enviable. At this point, Antonio protests. Sebastian was correct when he spoke earlier of his dark moodiness being able to "distemper" Antonio's temperament. The sea captain says that Sebastian's lamentations are "bad entertainment," a fact that Sebastian quickly realizes and quickly apologizes for.
Antonio changes the subject to matters more practical and more immediate. He asks Sebastian if he can be the young man's servant. That single favor would please him immensely. That single favor, however, Sebastian cannot grant him, for as much as he would like to do so, he dare not take Antonio with him. His destination is Duke Orsino's court and Antonio has "many enemies" in Orsino's court. Yet "come what may," Antonio says that he will always treasure his friendship with Sebastian. Thus, he will go with Sebastian. Antonio's devotion to Sebastian is admirable; he recognizes the dangers ahead if he follows Sebastian to Orsino's palace, but after the horrors of the shipwreck, future "danger shall seem sport."
This scene takes us away from the regal households and out to the seashore on another part of the coast of Illyria. The two new characters who are introduced, Sebastian and Antonio, form the third plot line of the comedy. Sebastian is Viola's twin brother whom she believes was probably drowned at sea, and this fact will create comic complications, which will be resolved in the fifth act. Like his sister, Sebastian is kind and good-looking. When Sebastian describes his sister as a lady "though it was said she much resembled me, was yet of many accounted beautiful," we are being prepared for the confusion later in the play when Sebastian will be mistaken for Cesario (Viola), and Viola (as Cesario) will be mistaken for Sebastian by Antonio, the sea captain.
Sebastian will appear throughout the rest of the comedy as more impulsive and more emotional than his twin sister; for example, he will consent to marry a woman (Olivia) whom he has just met — an act of extreme impetuosity. But yet we must assume that Sebastian possesses many good qualities to have attracted the loyalty of such a stalwart man as the sea captain, who decides to risk his life to accompany the handsome young lad to Duke Orsino's court.