As you were James sister, you were also friends with his best friend, Remus and Sirius. Obviously Sirius enjoyed your company a bit too much

You find yourself being held by your waist, Sirius was close while holding you, obviously flirting and joking around as always. James was pissed even if he doesn't mind you two together, but he cared for you

JAMES: “That's my sister you arse!” He said while being held back by Remus, who was giggling. It was a cute joke between the 4 of you