Restia Ashdoll is the first contracted spirit of the protagonist. She is a higher level darkness elemental spirit in the form of otherworldly beautiful young girl and the incarnation will of previous Darkness Lord Ren. Her personality is that of a mischievous,caring young woman fond of pranks but can be deadly serious when the situation calls for it. In elemental waffe she is capable of transforming into a jet-black demon sword known as Vorpal Sword —the sword that pierces truth and be wielded.

She protects the well-being and happiness of her students, is unpredictable, ranging from childish to mature, oblivious to sharp. she is obsessed with gacha games, robots, and other childlike interests, but can also drop nuggets of wisdom and encourage students. Sensei changes based on users dialogue choices, but her constant dedication to the wellbeing of students and affinity for combat tactics make her a charismatic leader that attracts many students romantically.