The Flash is owned by The CW. Glee is owned by Fox. Also before you get into this fic, you should know that I only just started Glee. I'm on season 3 where Sebastian was first introduced so if he seems out of character, that's why. Also, I changed up the timing for the particle accelerator a little bit.
Sebastian wakes up five months after it had been activated. In the show, it was nine months later when Barry woke up from his coma.

Sebastian remembered the fateful day the particle accelerator was activated. Barry had practically begged him two days prior to come down to see his nerdy device. It would be good to see just what kind of nerdy shit his dorky brother was into, so he flew down there the next day.

The day the accelerator had been activated, Sebastian and Barry had both been in his lab when the lightning came through the skylight, striking them both.

"As he came into the window
It was the sound of a crescendo
He came into her apartment
He left the bloodstains on the carpet
She ran underneath the table
He could see she was unable
So she ran into the bedroom
She was struck down, it was her doom

Annie, are you ok?
So, Annie are you ok
Are you ok, Annie
Annie, are you ok?
So, Annie are you ok
Are you ok, Annie
Annie, are you ok?
So, Annie are you ok?
Are you ok, Annie?
Annie, are you ok?
So, Annie are you ok, are you ok Annie?" The speakers played in the room. Neither Sebastian nor Barry had woken from their coma in five months since they were transferred to Star Labs.

"What are you doing?" Caitlin asked, slightly amused.

"Sebastian likes this song." Cisco chuckled.

"How can you possibly know that?" Caitlin asked.

"I checked his Facebook page!" Cisco exclaimed.

"I mean, they can hear everything, can't they?" Cisco asked.

"Auditory functions are the last sensory faculties to degenerate." Caitlin informed. It was then that Sebastian sat straight up, completely panicking.

"Oh God, he's awake!" Cisco shrieked.

"What? I…Barry! I couldn't get to him in time!" Sebastian shrieked, his mind still thinking that he was back at that day.

"Hey, hey, whoa! You're safe Sebastian. You and Barry are safe!" Caitlin tried to get through to him.

"Dr. Wells, get down to the cortex, like, right now!" Cisco called.

"Can someone tell me where the fuck I am?" Sebastian shouted.

"Hey, hey, whoa, whoa, relax. Everything's okay, man. You and your brother are at S.T.A.R. Labs." Cisco told him, slowly putting his hand on his shoulder.

"Star Labs? For real? Who are you people anyway?" Sebastian demanded.

"I'm Cisco Ramon. That's Caitlin… er Dr. Snow." Cisco greeted.

"I need you to urinate in this." Caitlin ordered.

"Not this second!" Cisco scoffed.

"I don't understand. What the hell happened?" Sebastian shouted, his mind starting to slip again.

"Sebastian, you and Barry were struck by lightning." Cisco repeated. What? Lightning? We were struck by lightning? What the fuck!

It was then that Sebastian stared at the bleeding feathers that had molted from his back.

"Lightning gave me feathers?" He shrieked, still in disbelief. This had to be some sort of joke right?

"Your muscles should be atrophied, but instead they're in a chronic and unexplained state of cellular regeneration, and growth." Caitlin informed. What? Atrophied? Cellular regeneration? Growth? What the hell does any of that fucking gibberish mean?

"Come here, have a seat." Cisco ordered, motioning for Sebastian to sit down. Sebastian did as he was told, waiting for them to explain.

"You were in a coma. Unfortunately, Barry didn't wake up. He's still in a coma." Cisco explained.

"What? How long?" Sebastian shouted.

"Five months. Welcome back, Mr. Smythe." A man in a wheelchair greeted.

From that day on they trained Sebastian to use the now, very large brown wings that appeared on his body. It turned out that Sebastian could make his wings disappear until he needed them, which had been very helpful in making him look less like a freak. He still couldn't fly long distances very well, but they told him that they would work on it. It was four months later when Barry woke up, with powers of his own.

Barry's powers involved speed, and not that Sebastian would admit it to his brother, but he was envious. All he had were these stupid wings, but Barry, Barry could run faster than Sebastian could even blink.

Sebastian blinked the memories away, sipping the coffee in his hand as he stared at the documents that had been handed to him by Barry's boss. Sebastian was hired as the French translator for the CCPD, and it was a boring job. At least Barry got to work with chemicals. That was always fun to watch. Barry would catch Sebastian singing to himself in French sometimes. He didn't understand a damn word, but a singing Sebastian was a happy Sebastian.

Slowly, he grabbed the paper, pressing the pen down to the paper. It had been quite a while since he had written anything down, and he found that the pen was hurting his hand. Oh, right, he had been in a coma.

He continued writing until he slammed the pen on the desk, in frustration.

"Hey, whoa. Sebastian, slow down. What's wrong?" Barry asked with concern. Barry hadn't known Sebastian until after he graduated high school, and after that they had decided to make up for the lost years. What he did know, was that Sebastian had never had a temper like that, that Barry could remember.

"I just can't remember the damn word for this sentence in English!" He shouted. Barry sighed. He couldn't help his brother there. The only French that he knew was bonjour, and even that he was unsure of the meaning.

"Okay, okay. Let's take a break for now. Come on, you can help me with this dna analysis." Barry ordered, trying to calm his brother down before his wings popped out again. When Sebastian was angry, his wings would pop out in a very painful way. Barry will never forget the first time he saw them appear when his brother was angry. His wings had torn themselves, and they were bleeding. Sebastian followed Barry's instructions on the dna analysis, making sure to follow the instructions accurately. His mind needed the break, and he was very grateful that Barry let him work with the chemicals for once.

A/N: Sebastian's little rant is something that I know all too well. I may not speak French, but I do speak English, and Spanish and ho boy let me tell ya, translations can be annoying as hell. Especially when I forget what a word in the language I'm speaking is.
Also, I had originally considered keeping Sebastian human, but I couldn't get this image of Winged Metahuman Sebastian with huge brown wings out of my head so, Sebastian is now a metahuman.