My Monster Secret: Aizawa Nagisa

Nagisa is a classmate of Asahi and Yōko, and is also a small alien riding a human-sized robotic exoskeleton of herself. Initially the love interest of Asahi before the series began, she turned him down before he could confess, believing that her secret would be discovered if she started a relationship with him. She, like most of Asahi's friends, is aware of his feelings for Yōko, and develops feelings for him after the fact. Her alien species is militaristic, and she often uses military terminology when describing things. Her exoskeleton runs on an internal battery that must be constantly recharged with an AC outlet and has on many occasions run out of power for comedic effect. She is usually meticulous and serious with her actions, though loses her composure when dealing with embarrassing situations. Nagisa has an older brother, Ryō, whom she initially respects and draws inspiration from, before learning he is less reliable than she initially realized. As a small alien, she is always wearing the same clothes her robot is wearing. Her exoskeleton has a metal screw cockpit opening with an antenna sticking out of it, but no one guesses what she really is despite this. When Yōko and Asahi start to date, she decides to put her feelings aside to help them, and remain friends.

My Monster Secret: Yōko Shiragami

Yōko is a classmate of Asahi and the daughter of a human and a vampire. Though she has long canine teeth, many other typical vampiric characteristics are downplayed, such as only getting tanned in sunlight or feeling guilty when entering a room uninvited. She has a Kansai accent, but speaks in honorifics so as not to expose her teeth. While initially coming across as haughty, her true personality is bubbly and absent minded. Her dream is to become a cool beauty, but has yet to accomplish this goal. Though initially friendly with Asahi, she develops romantic feelings for him, but keeps them to herself because she believes Asahi likes Aizawa. She is also often hungry, due to not being able to eat lunch for fear of revealing her teeth. As the series progresses, Asahi and Yōko begin dating, and accidentally becomes pregnant with Asahi's child after regularly sucking his blood, unaware that for a vampire, sucking a person's blood has the same effect as sexual intercourse. GIF made by Joachim361