You (Atsushi), had just been injured in battle. Slashed across the chest. It ripped your button up and your binder, but you didn't bleed too much. It didn't open your button up, but it did part your binder. Akutagawa wasn't convinced you were fine & didn't want his partner dying on him, so you were backed into a corner while he tried to convince you to unbutton your shirt so he could checkout the wound. You didn't want him knowing your trans..