Koishita Hito wa, Imouto no Kawari ni Shindekure to Itta. Imouto to Kekkon shita Kataomoi Aite ga Naze Imasara Watashi no Moto ni? To Omottara

Bright looks Wisteria dead in the eye, his gaze unwavering, and asks her to die in her sister's place. That's the setup, and it only gets more emotionally devastating from there. Lady Wisteria has been in love with Lord Bright for years, but he's devoted to her younger sister, Rosalie. When Rosalie is chosen to enter the Predawn Realm as its eternal guardian — a one-way trip — Bright begs Wisteria to go instead, since she's the one with the magical talent and miasma resistance. So she does. She takes the sacred sword Sartis and walks into what's essentially exile, heartbroken and alone. Then twenty-plus years pass. Wisteria has been living in this hostile magical realm for decades when a stranger who looks eerily like Bright shows up, demanding the sword and picking a fight. And now she has to deal with whatever this is on top of everything else. The story is built around unrequited love and sacrifice, but not in a melodramatic way — it's more quiet and introspective, sitting with the weight of what it means to give up everything for someone who never chose you. If you liked the emotional complexity of Yona of the Dawn or the world-building gravitas of The Twelve Kingdoms, this hits a similar nerve. It also carries some of that classic Fushigi Yûgi energy where fantasy and romantic heartache are completely inseparable. Based on a light novel, so expect layered character writing and a slow-burn narrative that rewards patience.