[Sweet romance + devoted to each other + multiple couples]
The heroine suffers from insomnia and unexpectedly transmigrates into a book, becoming the male lead's beloved.
In her previous life, the original owner married someone else but was never happy.
Given another chance at life, he won't let her go again.
She falls into the web of love he has carefully spun, utterly spoiled by him.
He gets jealous just because someone else calls her “big sister.” When night falls and no one is around, he turns into her younger boyfriend and keeps calling her “big sister.” Who could possibly resist that?