What should one do who has watched and read much translated anime and manga, which is not available for purchase, regarding the rights of their owners, and is it obligatory to buy them?

It is not permissible to watch or read copyrighted materials, whether visual or textual, without the permission of their owners. As for translated materials, mere translation does not make the translating entity the owner of the copyrights, and therefore, the obligation to seek permission from the owners of the original materials does not cease.