Doumo, Zense de Satsuriku no Madougu wo Tsukutteita Shishaku Reijou desu.

The viscount's daughter, Chloe, was the chief magical tools artisan for a country that perished a thousand years ago in her previous life. On the country's orders, she had created many weapons of slaughter. She laments her previous life and decides to, "live a respectable life this time." One day, at her graduation party, her best friend's engagement is broken off because of a lie. Chloe tries to save her best friend by unraveling the truth. (Source: Kadokawa, translated)