Yoku Wakaranai keredo Isekai ni Tensei shiteita you desu

The orphan Ren was riding the carriage after being sold, when she got involved into an accident, and got her previous life's memories back!

"I was... a middle-aged man!"

Indeed, she was a researcher in his thirties in her previous life, and had been living as an orphan girl up to now! Ren will make use of her talents in magic and knowledge in science to survive in this harsh world in order to escape from the investor who bought her!

(Source: Kodansha, translated)