Yomei Wazuka na Kodomo no Mamahaha ni Narimashita

After the death of her parents, Countess Clarisse lost everything to her uncle's family. To claim the only inheritance her parents left behind, she must recover the family heirloom, the magic stone, that was sold off. The one who now possesses that stone is none other than the ruthless Duke Albert, rumored to "use even children as tools of war"! But now, that very ruthless Duke is raising a baby with a rattle in his hand instead of a sword! Unaware of this, Clarisse visits the Duke's estate to strike a deal, only to encounter the dying infant, Theodore, and discover that she alone has the power to save him. Seeing her worth, the Duke offers her a deal: to become Theo's mother figure and in exchange, he will return the heirloom. But despite thinking she no longer needed a family, Clarisse slowly finds everyone around her starting to become obsessed with keeping her!