Responses
in some japanese elementary schools, there's no uniform. Riku is never shown wearing a boys uniform then or as a high schooler. In elementary school she simply wore pants because she was sporty. When Nobara meets her again, we only ever see her from the waist up. Her baggy sweater is gender neutral. At NO POINT is she shown wearing a boy's uniform.
If i'm wrong reply with a link to the page where she is shown wearing boys uniform.
They keep saying both "HE" and "SHE" for Riku...I think their a he cuz of the male uniform but idk man genderz.