For thousands of years humans have been the top of the food chain. This was the way of life, but In the shadows lurked genetically superior creatures. They looked like humans but they were genetically stronger in every aspect. This race of people hid within humanity's walls. Going completely unnoticed for thousands of years. Humanity, unknowning of their existence let them grow stronger throughout the generations. Their numbers grew and grew. As their population so did the Humans. Life was mostly peaceful for them as they didn't hurt humans. In over the last few hundreds of years they emerged from their hiding.
Revealing themselves to humanity. Finally, in act to be accepted to society. Humans were disgusted, they called them monsters. Branding them as the "Dragón". Although the Dragón were genetically superior, they treated humans as their equals. Showing kindness. They only hid because of the fear of persecution. Peace, loving creatures. Humans meet their kindness with the very thing they feared. Persecution. In act of rebellion they formed an organization known as the "Sigilark". They hunted the Dragón down. The Sigilark just starting out wasn't the most successful but they managed to kill hundreds of Dragón.
To become more proficient they used the corpses of dead Dragón creating new materials. Within the bodies of Dragón, their bones would be composed of different material compared to humans. Stronger, denser, and even shinier.
Their biology as a whole were completely different from humans. They had an organ in their body that released a biological weapon created by their bone and skin tissue. They called it the "Cero". The cells in their body were also reactive to this organ being the key to which it activates. The higher concentration of the Dragón cells, also known as D-Cells, would constitute the activation of the Cero. These bioweapons were superior to any man-made weapon. The Dragón finally started fighting back with the help of their Cero.
So using the corpses of dead Dragón only led to the creation of the Sigil weapons. Weapons crafted from the bones and Cero. The Sigilark's power only grew. Hunting down more and more Dragón.
Even now, the Dragón fight back against humanity's persecution. Developing a taste for human flesh. This change in their chemistry shifted the balance. They became driven for this new delicacy. Human Flesh. In the current era Dragóns have grown in size but the Sigilark work everyday to keep them at bay.