You're referring to the popular manga and anime series "Dragon Blood: Ryū no Noroi to Seieki de Kami" (also known as "Dragon's Blood")!
: The primary goal is to dismantle the divine order. This involves hunting down "Kami" (gods) and consuming their essence to strengthen the dragon's curse. The "Dragon Blood" Power System dragon blood ryuu no noroi to seieki de kami
In many traditions, the blood of a dragon is toxic. It is the physical manifestation of the creature’s rage and the corruption of its flesh. In the Nibelungenlied (Germanic legend), the hero Siegfried bathes in the blood of the dragon Fafnir. While this renders his skin invulnerable, a single linden leaf falling on his shoulder creates a fatal weak point. In modern interpretations, particularly within Japanese media (anime, manga, and light novels), this "curse" often manifests physically. Characters may develop scales, reptilian eyes, or a loss of humanity. The "curse" represents the cost of power; to hold the strength of a god, one must risk the mind of a beast. You're referring to the popular manga and anime