Baka to Test to Shoukanjuu‎ - Volume 7.5, Our Song by Tsunemura Yuusaku

Shu Yu transmigrated and became the original novel’s violent and brutal female Demon that caused the supporting male character, AKA hidden Boss, to become batsh*t crazy. However, right now, the Boss is just a lowly slave that was just given to her. What should she do?

- Description from Novelupdates

I was on my way home with my friend when suddenly, I spotted a catgirl cosplayer who made my heart skip a beat.But something felt off—I couldn’t recall seeing her in any anime, manga, or games I had ever come across. Confused, I asked my friend standing next to me.To my shock, his response sent chills down my spine:“Huh? What catgirl? What are you talking about?”Suddenly, a truck came barreling toward the girl. Without thinking, I rushed to save her. In the end, both of us were hit by the truck.Now, I find myself reincarnated in another world—in the body of the very catgirl I had seen.But... who is this girl?How is she related to the dungeons that keep popping up in this new world?

He doesn’t know why his mind has been transferred into that of a petty thief named Soran within the VRMMO . The new ‘Soran’ though possesses both the body’s previous occupant’s memories and his own. Using his experience as a Legendary Rogue who had reached the apex known as the Realm of Legends, he will now have to survive in this world which had once been a game to him.

When he heard the immortal sister from heaven had died, Fang Ren didn't really care.When he heard he was going on a blind date, Fang Ren was a bit concerned.When he heard his wife-to-be was the deceased sister from heaven, Fang Ren cared a lot!