The Reason Why My BF Became My Older Sister's Husband

Love and work were going well...until that incident on her 25th birthday.

Aiko Miyata lost her parents when she was very young, but she was enjoying her life with her kind older sister, Saeko, and her excellent and warm-hearted boyfriend, Yuma Yoshimura. On the day of her birthday, Aiko is stabbed by a hooded man who seems to be at the height of his happiness. From that day on, Aiko is caught up in an unimaginable tragedy...?