By fantastic elements I am going to assume you mean elements of fantasy. The elements are ones of the house as a human. The entire story is a wonderful representation of personification. Examples of this are embedded throughout the story, such as "It quivered at each sound, the house did." In fact, it is a unique story in that the house is the main character. It is the house that changes through the course of the story, experiences conflict and a sad resolution. There are robots that run the household. These are things we do not have in the modern world but Bradbury saw for the future. From the mice that come scurrying out to clean everything to the wildlife that comes alive in the nursery, all of the elements in the home are invented by the writer and therefore fantastical.
The vision of the future, as presented by Bradbury, is that nature will go on, as it always has, and that man and his creations will fall away and be forgotten. This is reflected in the Teasdale poem that the story was titled after,
And not one will know of the war, not one Will care at last when it is done.
Not one would mind, neither bird nor tree, If mankind perished utterly;
And Spring herself, when she woke at dawn Would scarcely know that we were gone.
This is the irony of the story. Man built this fantastical home to take care of all it's needs. Yet, man was destroyed by a nuclear bomb and nature took over, eventually, destroying the house. It could not save itself or the humans whose shadows were burned into the outside wall.
Ray Bradbury's There Will Come Soft Rains" is named after Sara Teasdale's poem, which hauntingly addresses the end of mankind. The story follows a day in the life of an automated house that continues to perform its duties after its owners have died in a nuclear war. It starts with an automated voice which acts as the morning alarm, announcing the time; breakfast is fixed, served and disposed of with no understanding that there is no one to give breakfast to. The house performs its daily work as usual, even though no one is there to enjoy the fruits of its labor. The only living thing mentioned, a dog, shows up briefly and then dies of radiation poisoning. One of the more grisly images is the family's silhouettes burned into the side of the home, a thinly veiled reference to this very occurrence when the United States dropped the atom bombs at the end of World War II. This story isn't exactly optimistic about the future of mankind; indeed, the deceased owners of this home appeared to have virtually every comfort and luxury possible, right down to the automated voice choosing and reading a poem aloud, (the Teasdale poem) but it couldn't save them from nuclear annihilation. Ultimately, the house also goes down in flames, unable to save itself, and the last thing the reader experiences is the house's haunting refrain as it recites the date over and over again.