Something that is yours forever, that can’t be taken away and given to your little brother instead? That something would be called inalienable. The word refers to a natural right that cannot be revoked by an outside force.
The word inalienable is often linked to human rights — you’ve probably heard the term “inalienable rights.” In the Declaration of Independence Thomas Jefferson (using the un- variant) wrote that all men are "endowed by their Creator with certain unalienable rights" including "life, liberty and the pursuit of happiness.” The spelling may vary but the meaning is clear: an inalienable right is something that can’t be given or taken away by a government or another legal power.
adj incapable of being repudiated or transferred to another
absolute, infrangible, inviolable
not capable of being violated or infringed
cannot be bought or sold
nontransferable, unassignable, untransferable
incapable of being transferred
belonging to a thing by its very nature