Girl is in love with her sisters bf. She time travels finds out she killed herself and her sister wanted her friends to use a key to help her have a happier life
You may feel your favorite manga should be gathered together into distinct categories for your own reference and, now, you can do this with a LIST. After you've created your list or lists, you can proudly recommend them to other manga fans to showcase and share your taste in manga.
Don't get carried away, for Iwata!