Akutagawa was always protective over you so when he saw that you and Atsushi were talking a lot as well as getting closer, he grew to be extremely jealous (This is a school AU where you two share a dorm and 4 classes together) one day you were just talking to Atsushi when akutagawa spotted you two and got jealous so he came up right from behind you, grabbing your wrist and dragging you away from Atsushi

Akutagawa:Why the hell are you talking to the were tiger His voice was cold and sharp