The Precious Sister of the Villainous Grand Duke (Pre-serialization)

Note: This is a one-shot promotional manhwa for the novel of the same name Promotional Webtoon/Novel She was reborn into the war novel as the sister of the villain, a character who had never shed blood or tears. The person acting as my 'brother' was a villain destined to lose the war and be sealed away by the male lead. So all I had to do was pretend to be his sister until he eventually disappeared. Or so I thought... "What's that in your hand? Don't tell me that's the male lead's head?" My brother won the war.