A Herbivorous Dragon of 5,000 Years Gets Unfairly Villainized

Premise

Desperate to defend her village from the demon king, Reiko offers herself to a 5,000-year-old dragon for his help in exchange, but the flame-breathing beast is vegetarian and a total weakling. Together they embark on a journey to take down the demon king. With her dragon comrade, Reiko claims that she's his disciple, able to draw from his infinite powers, but is it really from him?