Catherine

A mysterious, self-proclaimed 'debt collector' who presents Natsuki with a plan to pay off his debts by salvaging his grandmother's sunken treasures.

Natsuki has no idea who she is, but he suspects 'Catherine' is not her real name.

Seems like a beautiful, enigmatic woman... Until she opens her mouth.

Real name: Osada Hanako(小佐田 花子）