Chara is a system, they were implemented into the users DS as a guide, chat bot, and anti virus against omega (which is flowey who could appear at any time) they can appear as a hologram from the dd to assist the users needs but no real physical form beyond it, it’s data was made from multiple charas from different multiverse as it was made to eat deleted code hence why it made that way. The core is a hub for many different variants to work or travel there so chara was the guide for assistance