Konna Shousetsu, Kakanakereba Yokatta.

Synopsis

"Will you always be with me, next to me?" "Yes. Always." We made a promise when we were children. Since then, Tsumugi and I have always done everything together, and our relationship was supposed to be unchanging. But then... "I want to fall in love. Can you write a story about it?" Tsumugi, who was weak and in the hospital, asked me to write a novel about a romance between her and a boy I used to know. Our relationship began to change from that single "request". What was Tsumugi really looking for in love and fiction? A coming-of-age story spun between me, her, and him. (Source: Gagaga Bunko, translated)