Song used for the title and in the fic is "Must Have Done Something Good" by Relient k. Give it a listen, it's definitely something that needs to happen in canon.
"Kurt, hurry up!" came a shriek from outside the tiny bathroom in the loft. "We're gonna be late!"
"Just a sec, Rachel, God! I'd like for my breath to not kill people if I get too close!" Kurt yelled back after pulling his toothbrush out of his mouth. "Callbacks will still be there if we're a whole five minutes late!"
"But I had plans tonight, Kurt! I need to reserve prime karaoke time!" He could hear Rachel stamping her foot from her spot by the loft door.
"All right, all right, I'm here," he said, emerging from the bathroom in a flurry of annoyance and grabbing his lightweight jacket for the walk to the subway station. "Unknot your underwear and lead the way."
"There's no need to be snippy, Kurt. I promise you're going to have a great time tonight," Rachel replied snippily, buttoning her jacket and sliding open the door with an air of superiority that was unusual even for her.
"Whatever you say, Rach..." The last time Rachel had promised he'd "have a great time" when he went out with her he ended up watching her new crush Toby do a three-hour-long piece of performance art where he stripped almost entirely naked and covered himself in chocolate sauce and gummy worms. Needless to say, he did not have a great time and he wasn't going to trust her as far as he could throw her any more.
The crowd at Callbacks seemed to only be "slightly tipsy" and not "completely wasted," which wasn't too weird for only 8 pm on a Friday night. The hardcore drinkers wouldn't show up until about 10, and then they'd hog the mic for increasingly bad renditions of 80s songs and show tunes. Kurt was hoping to be long gone by then, but knowing Rachel, she'd probably manage to bum a drink from someone and then challenge everyone to a Barbra-off.
They found Santana and her choreographer girlfriend Lisa holding a table pretty close to center stage, though a few feet back so they could hold a conversation without screaming.
"When did you get here to hold this table, yesterday?" Kurt asked, astonished that they'd gotten into what was nicknamed "The Agent Area" amongst the NYADA kids. If someone important from a casting agency or record label was scouting, they'd immediately be seated at this table or either of the ones adjacent for prime listening/viewing potential.
"I'm a bartender now, Lady, I know people. I pulled some strings in order to give this sexy lady a great first time here," Santana snarked back, giving a quick smile to Lisa when she was done talking. The redheaded girl grinned back and moved to sit next to Santana instead of across from her, smacking a kiss on her cheek once she was settled. Rachel and Kurt took the other two seats available, with Kurt getting the seat directly facing the stage. They had just ordered their drinks when the first performer walked onto the stage, surprising Kurt.
"Wait a minute, that's-" Kurt started to say before the man onstage started talking into his mic, bringing the ambient noise to a hush.
"Uh, hi, everyone. I'm Blaine – you might recognize me from last fall when I sang a song to my now-ex-boyfriend, Kurt. I'm tired of that prefix being in front of his title, so I'm going to attempt singing him another song in order to win him back. Thanks for dragging him here tonight, Santana and Rachel – I owe you one. Guys, you can come out now," he called, prompting the other New Directions boys and Finn to come out and take their places around him, with Sam grabbing a guitar and Finn seating himself at the drum kit. "I hope you like this song, baby," Blaine finished, sitting down at the keyboard and lowering the mic stand to keep it level with his mouth. He nodded at the boys that he was ready to start.
"We should get jerseys, because we make a good team; but yours would look better than mine, because you're out of my league," Blaine started singing and Kurt clapped his hand over his mouth to keep his jaw from falling to the table. Normally he wasn't a fan of cheesy, somewhat-religious music, but he had a weak spot for this song and Blaine knew it. Last summer, before everything happened, Blaine had blasted this song on Kurt's iPod speakers and led them in a crazy dance around Kurt's bedroom, spinning Kurt around so many times that he'd thought that the world would never be still again. That relentless dizzy feeling was coming back full-force now.
"If anyone could make me a better person, you could! All I gotta say is I must've done something good. You came along one day and you rearranged my life – all I gotta say is I must've done something right, I must've done something right." Blaine had made it to the chorus at this point, with the other boys coming in with the harmonies to make the sound even fuller. Kurt's eyes were welling up at this point, though if anyone asked, it was because he was allergic to Rachel's hideous perfume.
For the rest of the song, Kurt alternately wiped tears away and smiled at Blaine, who was giving his all to the song like usual. Once it finished, Blaine spoke into the mic again.
"Kurt, I'm so sorry about last fall. I messed up and I know we can never go back to how we were. But do you think we could still make something good?"
"Of course we can, Blaine. I still love you so much!" Kurt stood up and yelled back at Blaine, over the crowd's increasingly louder chants of "Take him back!" and "Kiss him! Kiss him!"
"Should we give the people what they want, then?" Blaine smirked out at Kurt, moving over on the keyboard bench and patting the open spot next to him invitingly.
"You know I can't resist an audience," Kurt replied, walking up to the stage and sitting down next to Blaine before leaning in and planting a huge kiss on his lips. Blaine responded in kind, wrapping his arms around Kurt's waist and trying to slip in a little tongue before Kurt pulled back and whispered "Save that for when we get home, sweetie."
They slipped offstage and said good night to the boys before returning to Santana, Lisa, and Rachel.
"Oh, Blaine, that was so good!" Rachel effused, clapping her hands together a bit in excitement. "I'm so glad I could help play a part in your quest to win Kurt back."
"So that's why you were so afraid of being late, then, Rach? I suppose I can forgive you for viciously cutting short my bathroom time, since it did kind of get me my man back," Kurt said with a wink and a quick side-hug before crossing to the other side of the table and embracing Santana as well. "And that's why you called in the favor?"
"Only the best seats would do for Blaine-bo Baggins' epic journey to win back the gayest Von Trapp. Think of it as my thank you for the invite to the ballet gala last month. Also, that used up my niceness quota for the rest of the summer, so don't be asking me to leave the apartment when y'all want to get your kinky reunion sex on," Santana said, though the big smile on her face made it hard for Kurt to take her too seriously. "C'mon, Li, let's go get our grind on down at Ladyland now that the crown princes of Equestria have made up."
"Mind if we cut out early, too, Rach? I had a long flight today," Blaine said apologetically, unleashing a bit of his puppy-dog pout on her for maximum effect.
"Oh, get out of here. Maybe Finn will be willing to keep me company," she responded, looking around to see if he'd left yet and smiling when she saw him at the bar.
"I'm sure he'd love that, Rachel. Good night!" Kurt gave her one last hug and then stepped out of the way so Blaine could do the same. "C'mon, B, let's go home," he said, grabbing Blaine's hand and leading him out of Callbacks, kissing him once they were outside the building and he saw Blaine's tremendous grin.
"Home. I like the sound of that," was Blaine's first remark after breaking the kiss.
"Get used to it," Kurt replied, sneaking one last kiss before heading toward the subway station, Blaine's hand firmly encased in his.