Kaoru Asahina serves as secretary and assistant to Ryuichiro Isaka, a senior managing director at Marukawa Publishing. He handles organizational tasks and offers reliable support, though his strong sense of propriety occasionally compels him to intervene when Isaka's behavior oversteps boundaries. Asahina presents a formal appearance, typically clad in black suits with ties, sporting short brown hair and brown eyes, and standing taller than Isaka.

His past holds a defining trauma: a childhood incident where his financially ruined father attempted a family suicide via car accident. The Isaka family intervened, providing crucial support and employing Asahina's family. Designated as Ryuichiro Isaka's childhood playmate, Asahina's role evolved into that of a caretaker. During this time, Isaka gifted him an Amadokoro plant, symbolizing "cheer up" in flower language. This gesture prompted Asahina's first smile after the trauma, and the plant became a cherished possession he maintained for over a decade.

Their relationship developed romantically, though complicated by initial misunderstandings. Asahina's deep gratitude toward Isaka's father was misinterpreted by Isaka as romantic affection, leading to the "Junjou Mistake" label for their pairing. Asahina later clarified his feelings were always for Isaka himself, revealing he had loved Isaka since childhood. The pair became lovers, maintaining a committed relationship for over ten years and celebrating their anniversary within the series timeline. Asahina consistently addresses Isaka with formal politeness as "Ryuichiro-sama."

As adults, their dynamic balances professional duties with profound personal history. Asahina's loyalty and organizational skills make him an indispensable assistant, while his background as Isaka's childhood companion and long-term partner underscores their deep mutual understanding and emotional connection.