Paul Verlaine

Paul Verlaine is an ability-derived life-form created by the French researcher Pan, under whose servitude he was known as Black No. 12 (黒くろの１２号ごう). He later becomes a spy for France as trained by his eventual partner, Arthur Rimbaud. Originally the host of the singularity beast Demonic Beast Guivre, Verlaine possesses a gravity-manipulation ability, which he prominently uses in his assassination missions as the notorious King of Assassins (暗あん殺さつ王おう).

(Source: Bungou Stray Dogs Wiki)