Amazing story. Although I already have a feeling about the twist from the first chapter. So in granny's life Kiryuu is just her friend, but in the current life he become something more, so she won't end up alone later on.
I might be wrong here I think Grannies regret is her Happiness with Kiryuu, at the end she calls her "Friend" but here in the new timeline she is making him say I love you to her. Cause Granny lived alone as she said and her friend had a family of his own now.