Nemesis-chan

Who is Nemesis? Is she a bodyguard hired to protect the student that Ayano is after? Is she a vigilante who has made it her mission to stop Ayano? Is she another assassin who wants to remove her competition? Or, true to her namesake - the Greek goddess of retribution - is she here to take revenge on the protagonist for the sins of her past? For now, it's a complete mystery...