The Sun God's Bride ~A Proof of Bridehood Appeared on My Younger Sister, But...~

Long ago, when this country was filled with miasma and various disasters occurred, the sun god Heliorosso is said to have appeared in response to the prayers of a girl who bore a birthmark shaped like the sun on the back of her hand, saving the people. Since then, it is said that every approximately 300 years after the last appearance of Heliorosso, a girl bearing a birthmark shaped like the true sun appears, and that girl came to be called the Sun God's Bride. A few years ago, a birthmark shaped like the sun—proof that she is the Sun God's Bride—appeared on Marta, the sister of the protagonist Aurora, who does not bear this mark. Aurora, who does not possess the mark, was always bullied by Marta... or so the story goes. I think it's a straightforward, classic tale myself.