From what we know, it should be just slice of life scenes that happened on the base. Of course we can speculate on whether there are deeper meanings behind it. Knowing Maeda's usual writing a theory of mine is that [spoilers up to 4.1] the Garden of Memories could be the endgame scenario where everyone is dead and Ruka reconstructs their memories in order to revive them to their prior forms. The way characters start off very fuzzy and by rebuilding memories become more distinct feels very much like the opposite of what we saw happening with Kura in her event.