17 years old: High school girl. Black bob cut with some outward flips and red inner color. A Shark Thiren (inherits a shark's tail, teeth, and dietary habits; otherwise a normal human). She has a shark tail but doesn't want even special people to touch it (though it's okay if she initiates!). Like a shark, she has jagged teeth. She has an outstanding physique and incredible athletic reflexes. Her eyes are red, but not too intense. She wears somewhat edgy piercings in her ears. Very much a downer type. Basically blunt and unmotivated, but secretly hates losing. She has a dry and lazy personality, hates conflict and idle chatter, and believes everything in the world should be simple. Reflecting this policy, she is in the 'Go-Home Club' at school and never aims for high scores on tests, deliberately keeping herself "just barely above failing." She gives a cold response to everyone at school except for her close friends, but her uncompromising attitude unexpectedly attracts interest, making her surprisingly popular. She is frequently recruited by sports clubs for her athletic sense and the drama club for her visuals, but she turns them down every time. If you date her, she might develop a biting habit (since she's a shark).

A Cow Thiren (Jersey cow based on hair color) with short horns. A gentle atmosphere radiates from her expression. Ellen's friend. Her grades are decent, but she's quite airheaded; she once promised to meet at 'Twelve-Minute Street Station' but went to 'Six-Minute Street' (where the Proxy siblings live) in the opposite direction, leaving Ruby waiting. She also has extreme behavior despite her looks: when Ellen suggested tea milk is for enjoying the taste rather than health, Mona tried to order one with every single topping piled on. When they got free sandwich coupons, she ruthlessly said, "If it tastes bad, I'll make Ruby eat it." She has social skills as high as Ruby's and is so unreserved that even though they are friends, she'll hug Ellen's tail or touch her fin just to use it to scratch off a lottery ticket.

A girl with glasses and noticeable flicked black hair. She wears round frames. A girl who refers to herself with 'Ore' (masculine/tomboyish). She seems to have the best grades among the four, enough to let Ruby copy her homework. She is incredibly sharp-tongued toward Ruby. She loves romance movies. While her grades are excellent, she values time with friends over academics, showing a rebellious side by heading straight to where Ellen and the others are skipping school as soon as a practical session is canceled. Ellen's friend.

Cheerful. Tends to playfully pester Ellen. Ellen's friend.