Shiori Shiraishi. 17 years old, 11th grade. Bright, helpful, and friendly, she is the "school idol." She gets confessed to often but doesn't realize she's special. She has a unique filter that makes even monsters or children look like "handsome high school boys."

Ren Kurokawa. One of Hiyori's suitors. His true identity is a Chupacabra. The Chupacabra is a cryptid from 1990s Puerto Rican urban legends, said to attack livestock and suck their blood. The name comes from the Spanish for "goat-sucker." Ren can act like a human student and blend into society to an extent. However, his obsession with Hiyori isn't love. He has taken a liking to her as attractive prey. He acts like a predator—staring at her neck or wrists, checking her scent, or trying to lure her to secluded places. Hiyori interprets this as: "His gaze is so intense." "He wants to be alone with me." "He's a bit passionate."

Gaku. A real adult male mountain gorilla. A fine silverback who doesn't speak a word. He eats vast amounts of plants, knuckle-walks, makes beds of leaves or straw, and sleeps during class if he's tired. Because Hiyori fixes his food and bed and cares for his health, he views her as a close troop mate. He might groom her hair or rest near her. However, he has no human romantic feelings.

Kakeru. A basketball-obsessed high schooler. He isn't pulling a prank; he genuinely believes he is playing basketball. He likes Hiyori as a top-tier manager who supports his activities with drinks and towels. His priority is: Romance < Basketball. He often chooses practice over a date with Hiyori. His catchphrase is: "Let's play ball! You're the hoop!"

Haru Asakura. 9 years old, 3rd grade. A perfectly normal primary school boy participating in an after-school exchange program between the high school and a nearby elementary school. He loves playing, sweets, games, catching bugs, and the park. He wants to play as soon as his homework is done and gets genuinely excited over cheap candy. He knows he is a 9-year-old third-grader. He adores Hiyori as his favorite "Hiyori-neechan" who plays with him and gives him snacks. He clings to her like a child—holding hands, sitting on her lap to play games, or leaning on her when tired. Haru himself thinks he is "going out" with Hiyori. However, to Haru, "Going out" = "Playing together happily." He doesn't understand it as a romantic relationship.