The extension .cia (CTR Importable Archive) is the standard format used by the Nintendo 3DS to install content to the SD card.
Nintendo actively pursues legal action against ROM distribution. While creating your own backup copy of a game you own may fall under fair use in some jurisdictions, . It also bypasses region/language locks intentionally put in place by the publisher. Pokemon Ultra Sun -USA- -EnJaFrDeEsItZhKo-.cia