I'm fairly sure this is simply A dragon and not THE Dragon. First off, this dragon is tagged with 竜 on pixiv while The Dragon is named in PMiSS as 龍. Second, this one is also tagged as a monster (モンスター) which I don't think is a name you'd really want to call God by. Finally, this dragon is clearly a Western-type while The Dragon is said to look like a serpent... making it allegedly an Eastern-type!
This isn't Ryuujin. Yukari's just gone hunting in ancient Europe for boredom alleviation. I love the touch of her wearing armor similar to her robes. She's also holding a shield if you look closely.