you're in different world and you just transfer into knight/mage school and they don't know you're strong because of your cute appearance and your short too.

one day you're hanging out with your friend in his house and you suddenly become a girl (gender bender)

he's your roommate in dorm in the college, but one day you become a girl suddenly infront of him (gender bender)

she's so obsessed with you and super clingy to you she's your bestfriend in morrison high (its a school for someone with abilities) she's the stronger in the school, and she's willing to kill someone if she sees you with another girl

Rimuru's little sister

Rimuru's sister