The first time Kara saw Alex bent over her homework with her left hand curled around the mechanical pencil, she couldn't help but stare.

Alex felt the strange eyes on her and looked up. "What?" she asked.

"Sorry," Kara said, dropping her eyes down to the worn surface of the kitchen table that stretched between them. A flush of color rose in her cheeks.

Alex stared back at her now. Her new sister was weird.

Kara couldn't meet Alex's gaze. Her fingers traced the wood grain of the table, feeling the still-foreign sensation of its bumps and grooves. "There was a kid in my class back home who was…" She nodded toward the pencil in Alex's hand. "She learned to write with her right hand, though. I could help you, if you want."

Alex shook her head. "No, I'm good using my left," she said.

Kara's face turned even brighter red and she looked away. "Sorry," she apologized again. "Forget I said anything."

For fourteen years, Alex had had a bathroom to herself. She never knocked, never had anybody else hurrying her out so they could shower before school, never had to worry about whether the toothbrush she reached for was hers. But then Kara came.

Alex didn't mean to walk in on Kara getting out of the shower. She just… forgot that there was this other person in her space.

Alex walked into the bathroom and reached for her retainer case before she even spotted movement out of the corner of her eye.

"Um. Hi," Kara said. She stood naked and dripping on the bath mat. "Sorry, I didn't hear you knock." Kara hastily reached for a towel - Alex's towel, Alex couldn't help but notice - and wrapped it around her body.

Alex yanked her eyes away. She fiddled with the plastic case that housed her retainer. She hated that she had to wear it every night; even more so now that she suddenly had a sister with perfect teeth living in the room next to hers. "I forgot," Alex confessed. "Sorry for walking in on you." She hesitated. "Do mom and dad know?" she asked.

Kara's eyebrows knit together. "Know… what?"

Alex gestured downward. She didn't want to say it. Didn't want to make Kara uncomfortable by pointing out the fact that she obviously had a to her dismay, Kara didn't seem to register what she was referring to. "You know," Alex whispered, her cheeks burning, "your-"

"Girls!" Eliza Danver's voice carried up the stairs. "Lights out in thirty minutes, and you still both need to read tonight. Out of the bathroom and get in bed!"

Kara had arrived on Earth in the late spring, near the end of Alex's 7th grade year. Jeremiah and Eliza decided to keep Kara home for the last month of the school year, so she could have that time as well as the summer to acclimate to Earth before starting in the fall. The night before their first day of school, Alex slipped into Kara's bedroom after light's out.

"Hey Kara," she whispered. "You awake?"

Kara rolled over. She'd heard Alex's heartbeat pounding all through dinner, and had spent the last 10 minutes listening to her human sister pacing in her bedroom. "Yeah," she whispered back.

"At school, there's a, um, like a club. For people who are different."

Kara snorted. "Midvale Junior High has a club for aliens?" she asked.

"No," Alex said, "you know that's not what I mean. It's a… the GSA stands for 'gay straight alliance,' but it's for all queer kids. Kids that aren't straight. Or cis." Alex hesitated briefly, then forged ahead. "I know Mrs. Powell, the librarian, is in charge of it again this year. She said they were having the first meeting on Thursday after school. If you want… I mean, if you're…"

Kara felt a warm glow in her chest. Ever since she'd offered to teach Alex to use her right hand, and been rebuffed, she had avoided the topic of gender with her new sister. And Alex was her sister, even if she chose not to transition which hand she used. "I'd love to go with you, Alex," she said softly. "It means a lot that you asked me."

On Thursday morning, Alex told her mom that they needed to stay late for science club. The science club did meet that afternoon, and Alex planned to join, but today she wanted to take Kara to the GSA. And if Kara hadn't said anything to Alex's parents about being trans, than Alex certainly wasn't going to out her. She might still be getting used to her weird alien shadow, but protecting her new little sister was a job Alex took seriously.

To Alex's surprise, Kara met her right outside her classroom when the bell rang. "I thought your 6th period class was in D-block?" she asked.

Kara's lips quirked upward in a half-smile. "I walked fast," she said. "Not fast enough to freak people out!" she assured her quickly. The Danvers had talked with her frequently about the importance of keeping her powers hidden. "Just… fast. I wanted to meet you here. So I could walk with you."

Alex smiled back. She couldn't help it. She didn't know how to handle this, didn't know what she was supposed to say or do. But she couldn't help but feel happy that Kara trusted her with this. "Ready to go, then?"

Kara nodded and fell in beside her. "Have you been before? To the GSA?"

Alex shook her head. "One of my friends went for a bit last year, though. He said it really helped him." She reached for Kara's hand and gave it a quick squeeze. "It's a safe place," she promised.

She led Kara into the library and they found two seats together in the small circle of metal chairs that Mrs. Powell had set out for the group.

At the end of that first week of school, Kara was quiet. She'd been out with the Danvers over the summer, of course. They had taken her out when they ran errands, introduced her to some of their friends, and generally done a good job at easing her into human society. But in one week of school, she had interacted with more humans than in her whole first four months on this planet. And what she could see left her desperately confused.

The one trans girl she had known on Krypton worked hard to use her right hand, and suffered enormous anxiety about it when she was forced to use her left. Aunt Astra was ambidextrous - rare even among Kryptonians - although since she preferred her right hand she usually used "she" pronouns. Kara had been glad that at least she had some frame of reference for how deal with Alex being left-handed, but her efforts to reach out to Alex - to subtly convey her acceptance without making her sister uncomfortable - didn't seem to be making any headway. Alex didn't want to learn to use her right hand, even though she otherwise presented as a female. And although Alex had invited her to the GSA, then they had sat through the entire first meeting without either Kara or Alex saying a word.

And then there were the other humans. In the small Danvers family, from what Kara could tell, both Jeremiah and Eliza were cis: he was left-handed, and she right-handed. But from her observations through the first week of school, there were… a great deal more trans humans than Kara had expected. Most of her class seemed to write with their right hands - even people who obviously expressed a more masculine gender. And there were more than a few girls, like Alex, who used their left hands.

"Whatcha thinking about?"

Kara heard the popcorn that Alex tossed her way, and turned to catch it with her mouth open. "Nothing," she said. She wiggled her feet further under the blanket and grinned when Alex yelped at her cold toes. Kara reached into the popcorn bowl in Alex's lap.

She could have left it there, could have ignored Alex's inquiry and gone back to watching the wildlife documentary Alex had picked for tonight. But Kara glanced toward Eliza's office. The door was shut firmly, and Jeremiah still hadn't come home from work that night. "There's a lot of trans people at school," she said softly. "I knew humans could be trans too, but I didn't realize it would be so common." She watched Alex carefully, not sure if even bringing the topic up might be offensive.

Alex shrugged. "You mean TJ and Max from the GSA? I mean, that's two other kids in a school of, what? a couple hundred?"

Kara shook her head. Was it really possible that Alex hadn't noticed? "No, there are a lot more than that," she said.

Alex stared at her blankly for a second and then groaned. "Ugh, Kara!" she exclaimed. "I thought you were wearing the lead glasses so you wouldn't be x-ray creeping under everybody's clothes."

One day Eliza came home and told Alex that her aunt Jessica was pregnant. "It's a little girl," Eliza said, and Alex couldn't help but notice the way Kara's head snapped up, her attention pulled from her homework by Eliza's announcement. Alex cringed a little - her parents didn't know about Kara, but gendering a kid en utero in front of her still seemed insensitive - and told her mom to tell Aunt Jess congrats from her. She wasn't surprised when Kara approached her after Eliza left the room.

"I thought the baby wasn't born yet?" Kara asked. Jeremiah and Eliza had given her a synopsis of human reproduction - sperm meets egg and grows in a uterus. Inside a person. Natural reproduction had not been common on Krypton for centuries, although Kara had seen enough of Lara's pregnancy with Kal-El to know the general idea of things.

"She's not," Alex replied.

"So how do they know the gender?"

"They looked at the baby on an ultrasound and saw that she's got a vagina."

Kara nodded. "OK, but what does that have to do with anything?"

Alex sighed. "You're right. I mean, you can't really know the baby's gender until it's older. But most people assume if the kid has a vagina, she's a girl."

"What?" Kara's voice rose, incredulous. "What's a vagina have to do with it?"

Alex blinked. "It's… that's… I mean, some people are trans, so you shouldn't assume anyone's gender. But for the most part, if a person has a vagina, they're a girl. If they have a penis, they're a boy."

Kara laughed. "No, that's ridiculous," she brushed off Alex's explanation. "So on Earth, my penis makes me a boy? How does that even make sense? You might as well say it's whether someone has attached or unattached earlobes!"

"No, no," Alex rushed to reassure her. "I know you're a girl. You've said so since you got here. Even if you have a penis, that's okay, you are still a girl. Trans girls are girls."

"Hang on, so you think I'm trans?" Kara asked. She narrowed her eyes at her human sister, half-convinced by now that Alex was playing a joke on her.

Alex hesitated. "...aren't you?" she finally asked. "You have a penis. I saw it when you got out of the shower. And you wanted to go to the GSA and you talked about other trans people at school."

"Yeah," Kara blurted out, "I went to be there for you, because you're…" Her eyes dropped pointedly to Alex's left hand. "But I'm cis. I've always been right-hand-dominant"

"No," Alex shook her head. "How does which hand you use have to do with anything?"

"Girls use their right hands, and boys their left," Kara stated matter-of-factly.

"And having a penis means…"

Kara shrugged. "Means I've got a penis. Just like I've got light hair and you've got dark hair. Doesn't have anything to do with being a boy or a girl."

"But which hand you use does?" Alex looked at Kara carefully, not sure this wasn't all some Kryptonian idea of a joke.

"Of course. Babies don't have gender. Kids start showing gendered traits around two or hormones or whatever in brain development that cause kids to use one hand over another around that time are the same ones that then start to shape other secondary-sex characteristics."

"Seriously? So because I'm left-handed-"

"On Krypton, everyone would think you're a boy. Or… I mean, you identify as a girl. So you'd be a trans girl."

"But I'm cis," Alex stated.

"Because you have a vagina? But how does that… do people go around asking what type of genitals each other have?"

"No, you just… know. By how people look and how they dress and stuff."

Kara shook her head. "That seems like a good way to get it wrong a lot of the time. What about people who are ambidextrous?"

It took Alex a second to make the connection. "Nonbinary? Genderqueer? Like that? Most of the time people misgender them as either male or female. And then they have to correct them."

Kara wrinkled her nose in distaste.

"Ok, so maybe it's not the best system. But seriously, which hand you use? How is that any better?"

"It means I don't have to think about some stranger's genitals when deciding whether to call them Mr. or Ms. That's just… gross. And weird."

"I don't think anybody actually goes around thinking about people's genitals. It's more like… you grow up learning what men usually look like, and what women usually look like, and you guess people's gender based on that." Alex paused. "Yeah. Not the best system at all."