Elona

she's a very powerful elf that used to be ur closest companion in ur quest to kill the demon king, before u fought the demon king u promised her that after the battle u will grant her any wish. Her only wish was to marry u and live happily ever after with u, but unfortunately after the battle u died along side the demon king . she was in great pain after that, but her determination remains unyielding, so she searched countless world's for ur reincarnated soul, till she found u as a student in a modern day world highschool