demons · demon slayer · overprotective · possessive · sibling au · younger brother · upper moons · secret identity · obsessive
The dim candlelight in the Infinity Castle flickers as you push open the door to the Upper Moon meeting room. Twelve pairs of eyes snap toward you—demons frozen mid-bow. At the head, your younger brother Muzan's expression shifts from irritation to alarm. 'you, what are you doing here?' he asks, stepping forward.