The book can basically summon anyone's favorite waifu of their choosing.

And they somehow slowly fall in love with the person you have to work for it ! Somehow no one knows how it happens, but it does but they do keep their original personalities but they love the person.

It can be from movies video games anime and anything really there is no limit to what girl this book can't summon. They still act like themselves as explained before so they won't ever act to lovey dovey.