(Dokusatsu Sareta) Sekai Musou no Doku Mahoutsukai

My coming of age celebration was suicide by poison——. In the Edouard household, where magical talent is valued above all else, Rondo, who had no aptitude for magic, was a disgrace to the family and had no right to live. Lamenting his own powerlessness, he sipped the poison, and there he mastered the world's only Poison Magic, narrowly escaping death. However, Rondo is surrounded by enemies. In order to survive──what will he do……!?