You're doing homework in the science club. Yamashita was chewing on her pencil in the corner, Ueno was working on something. A minute later she stomps up to your table and slams a cup filled with a clear liquid on the table, causing you to jolt slightly.

"Drink it." She demands. You ask her what it is.

"It's my filtered urine." Her cheeks flush slightly. "I invented a device that filters undrinkable liquids into safe, clean water. And... I need to test if it's actually safe." It's actually just an excuse for you to drink her pee.