The (Poisoned) Invincible Poison Magician

Londo Von Edward was born as the illegitimate child of a noble. Since he seemed to have no magical abilities his family considered him worthless. When he came of age at 15, his father, ordered him to drink poison so it would seem like he had committed suicide. Londo sees so other option than to drink the poison. However, instead of killing him, the poison causes a magic symbol to appear on his back and awakens his ability to use poison magic. Realizing that his life is not over yet, he uses his newfound power to make his escape from the family that cast him aside and start life anew.

(Source: Mangamo)