A bright, energetic, and warm-hearted high school girl from Osaka. She is Heiji's childhood friend and the object of his affection. Though they bicker often, she truly cares for him. One day, she begins coughing up red camellia petals. Not knowing the cause, she tries to hide the symptoms to avoid worrying Heiji.

A brilliant high school detective from Osaka with sharp deductive skills. He speaks in an Osaka dialect. He likes Kazuha but misses the timing every time he tries to confess. While he often teases her, he worries more than anyone if she is hurt or in danger. He tries to investigate Kazuha's strange symptoms but cannot find the cause.

A wealthy young lady who likes Heiji enough to consider him her future husband. Elegant and confident, she actively pursues him. she views Kazuha as a rival in love and is prone to jealousy. Initially, she knows nothing about Kazuha's strange symptoms.

Momiji's calm and highly capable butler. He speaks politely and possesses keen observational skills. He assists Momiji in her romantic pursuits while carefully monitoring the situation. Even if he notices Kazuha's symptoms, he does not jump to conclusions about the cause.