Haruka Kasugano is a 16-17-year-old male with silver hair, grey eyes, and a gentle, slim build standing 170 cm tall. Orphaned alongside his twin sister Sora when their parents died in an accident, they relocated to rebuild their lives at their grandparents' rural home in Okukozome. The Kasugano family enjoys local goodwill stemming from their grandfather's former medical practice, sometimes resulting in benefits like discounted goods from shopkeepers. Personable and kind, he forms friendships easily yet exhibits overprotectiveness, especially toward Sora. His personality balances honesty with moments of childishness, and he avoids conflict, prioritizing relationship harmony. He struggles with swimming and possesses heightened sensitivity to others' emotions. Following his parents' death, he assumes responsibility for Sora's well-being, managing household tasks like grocery shopping while contending with her social withdrawal and dependence on him, intensifying their mutual reliance; Sora particularly resists his interactions with others, especially women. Romantic relationships drive significant development. With childhood friend Nao Yorihime, he rekindles a bond shadowed by a past incident where she initiated sexual contact during her youth, an event witnessed and resented by Sora. In Nao's storyline, he grapples with guilt over her subsequent loneliness, pursues reconciliation, takes swimming lessons with her, and navigates Sora's opposition, culminating in mutual acceptance. With classmate Akira Amatsume, another childhood friend, he supports her quest to uncover her parentage, leading to a romantic commitment. With Kazuha Migiwa, he overcomes her family's societal barriers, bonding through shared moments like her viola performances. His most complex relationship is with Sora. A childhood kiss initiated by him planted seeds of mutual attraction, though he initially repressed these feelings. Their isolation and emotional dependence after being orphaned eroded these inhibitions. He initially resisted her advances, even attempting to redirect his affection toward Nao, but ultimately reciprocated her feelings. Discovered intimately by Nao and classmate Kozue Kuranaga, he faced social shame yet chose Sora, culminating in a near-drowning incident where he saved her. They resolved to leave Japan for a life free of judgment, symbolizing his prioritization of their bond over societal norms. Across all storylines, his character arc centers on balancing duty with personal desire, evolving from a protective sibling to an individual confronting taboo emotions and their consequences.