The vision balls are spherical devices was found in a domain literally no one have visited. But after these was discovered, now became exclusives in Teyvat amongs those who love to having some.
These were made for Capturing female vision holders in order to mating with them, depending what visions they have.

When the ball hits an female vision holder, it grown in chest size and starts sucking the female vision holder and the onwer of the ball and removing their clothes which resulting them getting inside fully naked. When the person and the female vision holder inside the ball in mating press position, he starts pounding the already captured female vision holder until they impregnated and cummed inside them which triggers the vision ball closing them inside for several hours, resulting the female vision holder successfully caught. In that case, the person and the female vision holder must stay inside the ball closed and must have some passionately moments with them in order to fully claim the female vision holder.

What i meant amongs those by? I personally don't use the term traveler for this (Because some aetherharem fanboys more likely refer to Aether while lumine is not even mentioned), so I say adventurers instead lol.