I've been posting this on AO3 but I've decided to mirror it and post here as well.
Warning: Gratuitous Use of the Word Fuck

Other things: This is a hella slow build. There is character death much later in the story. Don't panic on me, Levi and Eren are 100% going to live.

Rating will be left at T for now but it will be M eventually.

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If you don't know what a stickleback is, be very happy. I wasn't a bio major but a bunch of my friends were and occasionally I'd help them out with their lab hours if they were running late.

Sticklebacks are boring as all get out.

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Eren was finally done with his rounds in the lab feeding the sticklebacks and jotting down all of the metrics and observation data. It had taken him longer than usual after he had knocked over the food that he had been pipetting into the tanks and had been forced to search though one of the neighboring labs to find more. It was almost dark out at this point and he felt bad cutting into his sister's night job since she always insisted on walking (well, flying) him home.

Mikasa didn't work any ordinary night job though. She worked as a superhero under the alias of Red Scarf. Since they weren't related by blood there was almost no chance that he would ever get super powers. When they were younger he had been jealous of her super strength and ability to fly. Her powers may not have manifested until she hit puberty, but she'd already been his protector even before then. Now though, he wasn't jealous so much as annoyed.

Eren's annoyance stemmed from the fact that his sister's occupation meant that he was kidnapped and targeted on a regular basis. He was his sister's weak spot and she would ditch a robbery if she thought that Eren had so much as stubbed his toe. It was a joke that he liked to tell but there was the one time when he had gotten into a fight with three guys on the way back from work a few years ago. The police hadn't been happy that she had left them to deal with the jewel thieves while she played hero for her idiot brother.

He was sick of it.

Being the "idiot" brother who couldn't stay out of trouble.

When he was younger he'd been a bit of a suicidal bastard; running into fights to defend people regardless of how much bigger or stronger than him their attackers were. He had mellowed out a lot (staring at fish all day will do that to you) but now he had to deal with being the target of almost every villain in Trost.

He was sick of that too.

But right now, he just wanted to get home. He had already told Mikasa that he would be late after the mishap with the spilled food earlier and she had told him to text her when he was done so that she could fly him home.

He took out his phone to text her and immediately dropped it into the stickleback tank right next to him. Sticking his hand into the tank to retrieve his phone he wondered if he could get superpowers from the genetically modified fish that he worked with on a daily basis. I'd probably just end up with powers like Aquaman. That would be humiliating. I think I'd rather just stay normal.

Staring at his phone he tried to think of what to do. He couldn't text his sister now. The school had taken the pay phones out of the lab building's lobby years ago and he had left his laptop at home, leaving him with no way to get in touch with his sister. I guess I'm taking the bus home.

Eren sifted through his pockets and then his backpack.

He was fifty cents short for the bus fare.

Scratch that. I guess I'm walking home.