Blackfire first appears in the episode "Mr. Butt". After getting into trouble with the Galactic Police again, Blackfire seeks refuge with her little sister, Starfire. After Starfire gave Blackfire delighted hugs, she introduced Blackfire to the rest of the Titans, who took an immediate disliking to her. After having Blackfire flirt with him, Robin pulls Starfire into the kitchen, and angrily tells her that Blackfire was one of the most wanted criminals, and the rest of the Titans agree. Starfire then claims that she was going to give Blackfire one more chance, but if Blackfire crushed Starfire's sisterly feelings once more, a thoroughly enraged Starfire would destroy her. After Blackfire grudgingly does "sisterly stuff" with Starfire (making Starfire look exactly like her), the Galactic Police find Starfire (dressed as Blackfire), and take her prisoner where Starfire, both heartbroken and revenge-torn, swears to destroy Blackfire once and for all. Blackfire is next seen silently watching Robin work out, while the Boy Wonder doesn't (but eventually does) notice, much to Blackfire's pleasure. Robin(after Blackfire tells him; "Did anyone tell you that you have a nice butt, Robin?"), sees Starfire is gone, but Blackfire is there, angrily demands for Blackfire to tell him where Starfire is.
When Blackfire tells him to relax ("Relax, Mr. Butt"), where the Titans see that Blackfire was a horrible older sister. Cyborg gives her a list of items to pick up, because she was going to 'Sister School'. After learning to listen to a sister's problems (listening to Beast Boy whine and yelling at him to 'man up'), how to hug a sister (after she refuses to hug the other Titans, she eagerly gives Robin a long hug), and how to live with a sister (the Titans dress up as Starfire and pester Blackfire), Blackfire feels guilt for her horrible actions toward her younger sister, and becomes a better older sister. In the midst of this, a thoroughly enraged and revenge-torn Starfire breaks into Titans Tower, bent on destroying Blackfire once and for all. Blackfire tries to help with sisterly loving actions, but Starfire makes it clear (after punching Robin, causing Beast Boy to exclaim; "Mr. Butt, are you okay?")that she wouldn't fall for that again. After pushing Blackfire through many buildings, Blackfire finally gets her to stop for a while by showing her the doll that Blackfire had stolen from Starfire as a five-year-old child, and apologizing for it, also stating "I've changed, now." Starfire, momentarily touched by the apology, remembers herself and says, "So have I.", and shooting Blackfire with an bright green starbolt eye blast. Later, in Titans Tower, Blackfire and Starfire appear in the main lounge, causing the Titans to jump up and ask how it went. After Blackfire faints from exhaustion and pain, Starfire cheerfully states that they had "worked things out."