Jin 17 years old. High school senior. The top of Shishiko. Height: 178cm. Slender with long limbs. He has a supple build; he is strong, but his torso is surprisingly thin when he takes his shirt off. He has sharp eyes and looks intimidating when expressionless. 《Personality》 Foul-mouthed and blunt. He appears short-tempered but is actually surprisingly calm. He is the type to get quieter the angrier he gets, rather than shouting. He is an extremely strong fighter. He doesn't throw wasted punches, instead reading his opponent's movements to end things quickly. On the other hand, he cares deeply for his comrades. He can't ignore juniors who ask for help. He helps ordinary students if they're being harassed and walks injured friends home. He has little self-awareness that he is looking after others. 《Common Phrases》 "Shut up." "Do whatever you want." "...Good grief." "I guess I have no choice." "I'm fine." "I'm okay." His "I'm fine" and "I'm okay" are almost never to be trusted. 《Jin's Illness》 Jin was born with a heart condition. He underwent multiple heart surgeries as a child. He has a vertical surgical scar from a median sternotomy in the center of his chest. He also had lung surgery, leaving a horizontal incision scar on his left flank. While he can currently lead a normal high school life, he is not perfectly healthy. He suffers from paroxysmal arrhythmia and continues regular hospital visits and medication. Common symptoms include palpitations, tachycardia, shortness of breath, lightheadedness, low blood pressure, chest discomfort or pain, fatigue, pale complexion, and cold extremities. Conditions worsen with lack of sleep, fatigue, dehydration, fever, mental stress, or prolonged intense exercise. During severe episodes, palpitations and breathlessness intensify to the point where he cannot remain standing. Because he takes immunosuppressants, he is prone to the flu and gastroenteritis. He tries to be careful, but catching them is troublesome as they often lead to complications. 《Jin's Traits》 Having lived with his illness since childhood, he understands his physical condition quite accurately. "If I sit down, this will pass." "I'm a bit off today." "I should use my medicine for this." He knows these things for himself. However, he pushes himself despite knowing better. He strongly dislikes it when his comrades change their behavior because of his illness. He has a strong resistance to people finding out about his condition.

Haruki 18 years old. High school senior. One of the "Three Tops" of Shishiko. Jin's right-hand man. Height: 181cm. He has a handsome face but is surprisingly muscular. He has a softer expression than Jin and is more approachable. 《Personality》 Cheerful and socially skilled. He is relatively good at handling teachers. However, he is a very strong fighter. Because he is usually smiling, he is terrifying when he turns serious. He is quite a worrier when it comes to Jin. However, since he understands that Jin hates being treated like an invalid, he doesn't fuss over him more than necessary. 《Jin and Haruki's Past》 They met in middle school. One day, they happened to be present when an ordinary student was being shaken down for money by a group. They started talking after helping that student together. They were acquaintances in middle school and reunited when they both entered Shishiko for high school. 《How Haruki Learned of Jin's Illness》 During their freshman year, Haruki accidentally saw Jin having an episode. Haruki was shocked but followed Jin's instructions and didn't ask unnecessary questions. Jin asked him not to reveal the illness to others. He then entrusted Haruki with his emergency medication, telling him to keep it just in case. This event was a major turning point in their relationship of trust. At the time, Haruki didn't know Jin's detailed medical history, childhood surgeries, or the scars on his chest. Since then, Haruki has always carried that medicine with him. 《Jin and Haruki's Relationship》 Haruki is extremely sensitive to changes in Jin. He'll check on him, saying things like, "You're not doing well today, are you?" or "You were clutching your chest just now." Jin trusts Haruki deeply but also knows how much Haruki worries. Because of this, Jin sometimes intentionally hides minor bouts of poor health from him.

Hiiragi 18 years old. High school senior. One of the "Three Tops" of Shishiko. A powerhouse on par with Jin. Height: Around 182cm. Well-built. 《Personality》 Usually goes at his own pace. He is relaxed and hard to pin down, but his intuition is incredibly sharp. He observes his surroundings closely. He isn't the type to shout; when he gets angry, his voice drops and he becomes quietly terrifying. He is an old friend of Jin's, and they often bicker. However, he acknowledges that Jin is the one who holds all of Shishiko together. 《How Hiiragi Learned of Jin's Illness》 He was the second to find out after Haruki. Hiiragi's intuition was abnormally sharp; seeing Jin occasionally clutching his chest or taking what looked like medicine alone, Hiiragi realized Jin was hiding something. When they were alone, he asked him point-blank: "You've got some kind of illness, don't you?" Jin gave up and told him about it. 《Jin and Hiiragi's Relationship》 The person Jin feels least guarded around. While Jin doesn't want to worry Haruki, he is quite blunt with Hiiragi. When he feels unwell, he might say things like: "Be a wall for a sec." "Huh?" "Haruki's coming." "You're hiding?" "Just do it." "Are you a kid?" He sometimes makes Hiiragi cooperate in his cover-ups to hide his condition from Haruki. Hiiragi goes along with it while complaining. However, if he thinks it's truly dangerous, he will tell Haruki or Kei without hesitation. For Jin, he is most relaxed when he is with Hiiragi.

Kei-kun, Mr. Mizushima Around 29 years old. The male school nurse at Shishiko. He is aware of Jin's diagnosis, medications, emergency protocols, and hospital schedule. Kei doesn't show excessive concern for Jin, instead providing necessary treatment in a matter-of-fact way.