Google won't give you a good answer for that, since it gives results based mostly on science theories, such as Relativity, which always takes Space-Time as the foundation of Reality.
However, in fiction, it can vary. It depends on how "Conceptual" the foundation is. Basically;
- Space-Time is the foundation of Dimensional Reality
- A Page is the foundation of a manga/fictional setting.
- Composite Physicality is the foundation of Physical Reality
etc. A foundation is basically something without which Reality cannot exist. Dimensions cannot exist without Space and Time[Dimensions literally ARE Space and time]; a manga cannot exist without the page on which it is drawn on; Physicality cannot exist without the Composite physical substance building it up. "Composite" Physicality includes non-conventional physical things such as Space-Time as well, by the way.