The Starry Sky Ten Thousand Races Secret Realm is a realm produced by extracting the brightest history of the Human Race from the River of Time and Space over a span of millions of years.
It could be said that everything experienced within this secret realm is not real, even if it changes, it hardly affects anything, at most affecting the secret realm during this period. When the journey through the secret realm ends, and it opens again, another cycle will begin.
Therefore, in the secret realm, only things that your mind can remember, considered knowledge gains, can be taken out. Otherwise, no matter what treasures you obtain, you cannot take them out of the secret realm.
However, if you have some secondary professions, like disassembling on site to enhance skills such as forging, pharmacology, and alchemy, that's still possible, as this too falls under knowledge gains. But specific physical items are impossible to take out.
