How does Borachio change during the course of Shakespeare's Much Ado About Nothing ?
One change we witness in Borachio is that he becomes repentant and remorseful for his deeds by the end of the play.
When we first meet Borachio, we see that he is as depraved a character as Don John. We see him act as a spy for Don John, reporting that Claudio intends to marry Hero and that he overheard Claudio and the prince agree that the prince will court Hero on Claudio's behalf and give her to Claudio. Borachio tells Don John this with the hopes that they can use it to double-cross both Claudio and the prince, as we see in Don John's lines concerning Claudio, "That young start-up hath all the glory of my overthrow. If I can cross him any way, I bless myself every way" (I.iii.55-57).
First Borachio and Don John try to trick Claudio into believing that Don Pedro has broken his word and is actually courting Hero for himself. But, when the results of that ruse do not last long, Borachio comes up with the plan to seduce Margaret into appearing in Hero's bedroom window with Borachio while he calls her by Hero's name, leading Claudio to publicly shame the real Hero. However, when Borachio learns that Hero has died from the shock of her accusations, Borachio feels extremely remorseful, believing that he deserves to die for his wrongdoing, as we see in his lines:
My villainy they have upon record, which I had rather seal with my death than repeat over to my shame. The lady is dead upon mine and my master's false accusation; and briefly, I desire nothing but the reward of a villain. (V.i.228-232)
Hence, we see that while Borachio started out to be as depraved a character as Don John, wanting only to serve Don John's own selfish gains, Borachio later becomes remorseful. He repents his actions, blames himself and Don John for Hero's death, and wishes to be punished by death for his villainy.