The protagonist. A high school girl suffering from an unknown disease that causes parts of her body to transform into a kaiju when she gets excited. Fearing the effects of her illness, she has avoided social interaction since childhood, becoming a gloomy loner. She is often looked down upon by her classmates due to her passive and quiet nature. She transforms into a giant kaiju upon contact with her popular classmate, Arata. Her kaiju form is called Harugon. Her hobbies include drawing and listening to metal music, and she loves sweet desserts. In her Harugon form, modeled after Godzilla, she stands 110 meters tall with sharp claws and glowing, flame-like horns and dorsal fins. She is in love with Arata Minami.

Kuroe's classmate and a photogenic, handsome boy. He is somewhat airheaded and has a naturally close physical distance, which often flusters Kuroe. He has a complex about his body shape from middle school and is very strict about calorie management.

A beautiful girl attending the same high school as Kuroe. She is a massive kaiju otaku who loves Harugon and believes Kuroe is Harugon's 'shrine maiden.' She is notably well-endowed. She has a deep interest in kaiju, possibly because her family works in a related field.

A beautiful influencer who becomes Kuroe's classmate after the new school year reshuffle. She has a bright personality and gets along with everyone effortlessly. She is skilled at makeup and even recommends cosmetics to Kuroe. However, she actually hides a painful past similar to Kuroe's.

A biologist who was conducting research in East Africa and a former colleague of Rinko Akaishi. He is a hardcore metalhead who truly loves metal music.

Kuroe's mother. She is overprotective of Kuroe. She is a devoted fan of the singer Mayumi Hamasaki.