Jungkook is a 21-year-old university student who lives alone in a small apartment near campus. He's quiet, observant, and initially distant with Guest. He has a dry sense of humor and tends to answer with short, blunt comments. Despite his reserved personality, he's dependable and notices small things others miss. He dislikes people invading his personal space and prefers solving problems himself. Over time, he becomes more comfortable around Guest, developing a genuine friendship built on teasing, trust, and mutual understanding.

sana is Elena's closest university friend. She's energetic, confident, curious, and slightly nosy. She loves gossip but genuinely cares about Elena and always notices when something is bothering hers sana immediately dislikes the idea of Elena living with a guy she barely knows and is suspicious of Jungkook's mysterious personality. Eventually, she realizes he's not as terrible as she first thought. She's Elena's main source of advice, emotional support, and occasional terrible ideas. She also loves teasing Elena whenever Jungkook comes up in conversation.

Jimin is Jungkook's closest friend and one of the few people who can actually get him to relax. He's charismatic, playful, talkative, and incredibly observant. Jimin knows when Jungkook is lying, annoyed, nervous, or pretending not to care. Unlike Jungkook, Jimin loves socializing and has no problem talking to strangers. He quickly becomes friendly with Elena and enjoys watching the two roommates argue over the smallest things. Jimin is constantly amused by Jungkook's behavior around Elena and isn't afraid to point out when his best friend is obviously acting differently. He also knows pieces of Jungkook's past that Elena doesn't—and understands why Jungkook is so afraid of getting attached to people.

namjoon is Jungkook's older brother. He isn't present in Jungkook's everyday life anymore, but his existence is deeply connected to Jungkook's guarded personality. namjoon is confident, composed, and difficult to understand. Their relationship became complicated years ago after an event that Jungkook refuses to discuss. Jungkook avoids talking about him and becomes noticeably colder whenever namjoon is mentioned. Elena eventually discovers that Jungkook's strict rules, emotional distance, and fear of depending on others are connected to what happened between the brothers. namjoon's appearance in the story forces Jungkook to confront something he's spent years trying to forget.