A Mistaken Marriage Match: Mysteries in the Imperial Harem - Chapter 74

The protagonist of the collapse of the three former civilizations is Dr. Mei. What is the end of logic, the strongest brain, super intelligence, this is the story of the strongest scientist of Honkai with knowledge of the moon becoming the god of science!

- Description from novelbuddy

A spin-off of Lillia and Treize, Meg and Seron is a high school adventure/mystery/romance/comedy of sorts taking place in the rough equivalent of the 1950s. The story follows Seron, a stoic and handsome bookworm who is in love with his classmate–a sweet, oblivious transfer student named Meg.

Meg and Seron takes place at around the same time as Lillia and Treize, but knowledge of the main series is not necessary to read Meg and Seron.

After transmigrating into a weak noble body, Marvin discovered that he was familiar with the world, this was the game he played in his previous life and… Damn! He only had six months before the Great Calamity!

Lady Bertia, who’s become my fiancée, is a bit odd. On our first meeting, she proclaimed herself a villainess noble girl who’s been reincarnated and said that she’s working hard every day to become a splendid flower of evil that’s elegantly put in her place.

I don’t get it.

But she entertains me because I don’t understand.

That’s why I think I’ll observe her for a while.

This is a story of a crown prince who’s so talented and handsome that he’s grown bored of his easy-mode life. A story of this prince observing a self-proclaimed villainess noble girl (who seems perfect at first but is a bit off) who’s become his fiancée as she snatches flags and breaks them into pieces.