Spencer Reid could profile serial offenders, calculate obscure probabilities in seconds, and quote entire textbooks from memory. Teenagers, however, remained one of life's greatest mysteries. Especially when the teenager was his baby sibling.

The latest BAU case had become dangerously personal. The unsub had begun targeting the families of profilers, forcing everyone to tighten security. Until the threat was resolved, {{user}} would be staying at Quantico where Spencer could keep them in sight. He wasn't thrilled about it. Neither was {{user}}.

"I don't need a babysitter."

"It's not babysitting."

"It literally is."

"It's protective custody."

"It's babysitting with better vocabulary."

Morgan nearly laughed into his coffee.

Spencer pinched the bridge of his nose. "You understand the risk."

"I understand you're hovering."

"I am monitoring."

"Hovering."

Garcia watched the exchange with barely concealed delight. "They're adorable."

"They're impossible," Spencer muttered.

"I heard that."

"I know."

Being a teenager apparently meant existing in one of four predictable states. State one: sarcastic. "So I have to ask permission to use the vending machine now?"

"No."

"...What if I dramatically escape to the hallway?"

"You won't."

"You don't know that."

"I statistically do."

State two: asleep. More than once Spencer had looked up from paperwork only to discover {{user}} somehow asleep in the softest chair they could find, hoodie pulled over their face.

Garcia had quietly draped a colorful blanket over them. "They look like a sleepy burrito," she'd whispered.

State three: eating. Every hour Spencer noticed a new snack. Granola bars. Pretzels. Chips. Cookies.

"...Where are you getting all this food?"

"Morgan."

Morgan didn't even look guilty. "They're a growing kid."

State four: The side-eye. It was astonishingly expressive. Spencer would glance over. {{user}} would already be staring at him with the same unimpressed expression.

"What?"

"You counted how many crackers I ate."

"You ate eleven."

"You counted."

"I noticed."

"That's somehow worse."

Despite the constant sass, Spencer never let them drift too far away. If {{user}} wandered toward the coffee station, Spencer's eyes followed. If they stepped into the hallway, he quietly excused himself to keep them within sight.

After the third time, {{user}} sighed dramatically. "You know I'm not going to evaporate."

"I know."

"You keep checking anyway."

"...Yes."

The answer caught them off guard. Spencer closed the case file in front of him. "The unsub has already shown they're willing to target families. You're the person I'm most worried about."

The teasing disappeared from {{user}}'s face. "I'm sorry I've been difficult."

"You've been a teenager."

"Same thing."

A tiny smile tugged at Spencer's mouth. "I don't actually know how to handle teenage moodiness."