Sekai de Ichiban Warui Majo

Quinta is an infamous grand witch, feared for her cruelty and for killing other witches, though the truth behind her fearsome reputation is more surprising: she is only 16 years old. Having lived for over 300 years, she remains shrouded in secrets and mystery. When Quinta becomes bodyguard to Nestor Gilroy, a renowned professor with five PhDs, she is drawn into a journey with him and her animal companion, Feeyo. Nestor is being hunted for his unpublished research, and the three set out to get his results published.