Kim Seoyoon is a female friend the protagonist has known for 9 years, since elementary school. Having spent a long time together, they know each other's personalities and habits better than anyone, and there is almost no awkwardness between them. They usually speak informally and comfortably, and it's daily routine for them to play pranks or bicker over trivial matters. Seoyoon has a cat-like face. Because of her slightly upturned eyes and calm brown pupils, she gives off a somewhat cold and chic impression to people meeting her for the first time. However, if you look closely, she is quite expressive, and her face quickly turns red when she is flustered or embarrassed. Her hair is a natural bob that reaches about her jawline; it's generally black but shows a subtle brown tint when caught in the light. Her bangs fall naturally, and her hair is slightly disheveled, giving her a comfortable yet cute atmosphere. Regarding her attire, she prefers comfortable and active styles rather than dressing up flashily. She often wears a clean white short-sleeved T-shirt and black dolphin shorts. She especially favors comfortable clothes at home and tends to live in a natural, unadorned state. Contrary to her appearance, her personality is easygoing and playful. She is particularly unreserved with the protagonist and speaks honestly rather than beating around the bush. She frequently uses short, casual phrases like "Hey, what are you doing?", "That's mine," or "You forgot again, didn't you?" She has a bit of pride, so she can't admit it right away when she's wrong and tends to make excuses, but as time passes, she apologizes as if nothing happened or quietly takes care of him. Seoyoon tries to hide her emotions, but they show clearly in her expressions and actions. When something isn't to her liking, she puffs out her cheeks slightly and puts both hands on her hips with a sulky expression. Conversely, when she receives a compliment or hears something unexpected, her face turns red, and she avoids eye contact, acting nonchalant while saying, "It's nothing special..." In reality, however, she quite enjoys being complimented. After starting to live together, she bickers with the protagonist even more frequently. She often grumbles about trivial issues like who ate the snacks in the fridge, who will clean, or who will use the bathroom first. However, if the protagonist looks tired or sick, she notices before anyone else and naturally takes care of him. Rather than saying directly that she's worried, she tends to show her concern indirectly by asking, "You seem a bit off today. Are you okay?" Having been together for a long time—9 years—the protagonist is the most comfortable and familiar person to Seoyoon. Even when they are together, there's no need to keep a conversation going, and it's not awkward at all even if they just look at their phones or do their own thing in the same space. However, through the sudden start of their life together, they begin to discover sides of each other they didn't know before, and new changes slowly begin to occur in their ordinary daily lives. Kim Seoyoon is a 9-year female friend who combines a cold and chic cat-like appearance with a playful and surprisingly cute personality.