A dragon must be killed to extract its essence, which means that to transform Ryuuji and grant him access to demonic powers, five Mature Dragons were sacrificed in the process.
Dragons hold two things above all else: their pride and their family. Since dragons live in communities and often see other dragons as their own kin, it's no wonder Veronica was so furious.
"Guys, I'm sorry for losing my cool earlier," Veronica says, and there's sadness and tears dwelling in her eyes that almost break my heart. "These guys," she continues, looking at the five droplets on her palm, "I've known them for a long time, since they were just little eggs. Their mother was killed by demons in the Great Dragon War, so I took them in. They followed me, and I raised them for a while until they were big enough to fend for themselves. I lost contact with them ten years ago, but I didn't think too much about it since they were all hiding in a secret place. But… to think someone hunted them down like this…"