The Science-Minded World Without Conan

Before being adopted by the Kudo couple, Kudo Shinki had already been adopted three times. For some reason, all sorts of things kept happening, and every time, she was sent back to the orphanage. But just before she was about to be sent back for the third time, Kudo Shinki met a nice girl named Mori Ran. Somehow, she ended up becoming the newest member of the Kudo family.

Hmm (=?Д?=)

Come to think of it, she seems to have a big brother, the Kudo couple's biological son and Mori Ran's childhood friend. But why has she never seen him?

And she's supposed to be a child, right? Yet from the way the adults act, Shinki can't help feeling like they treat her as an adult! Though whenever danger comes up, people do protect her! Especially her big brother's childhood friend. She's way overprotective!

The protagonist lost her memories after a head injury, and for some unknown reason, she also changed sex.

Theme: A gender-swapped protagonist.