previous ch, MC got attacked by MC's body's older brother and got her core taken
in an even older ch, the "doctor" was introduced and was the one who put MC into their current body (from what i can remember)
"doctor" made hero use alchemy to cure MC, and gave MC an artificial core that also...
the Gender Bend tag seems like an afterthought
"oh i have memories as a high school boy from a past life", proceeds to not have anything to do with them