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Devil x Bride ~Which daughter is the chosen one?~

"As promised, I came to pick you up on your 16th birthday, my bride."
Twin daughters born to an earl family.. One of the two must become the "devil's bride".
The contract with the devil that their grandfather made was the trigger that changed the fate of the twins.. Twins who don't know anything and spend their days peacefully.
But suddenly, a "devil's pattern" appears on the younger sister's hand, and everything changes completely!
The younger sister receives all the attention and love from her family, and the older sister is isolated and ignored by everyone..
The growing sister gap.
"I'm sure this world was wrong even before I was born and fell..."
Kurumi Hanari, a master of human drama, creates short stories that are very popular in "Let's Become a Novelist."
A story of cruel fate depicting the disparity between sisters!

I bought this one because of the nun on the cover, I thought it would be a hentai. It isn't, rather it is a ladies' comic. A serious one it seems. I don't know what the story is about.
Anyways, here it is for you guys to enjoy I guess.