dopplegamer

A dopplegamer (noun) are two people who shares a common steam library, or game genre that comes into contact and immediately become friends through a single conversation over their favorite games. After such activities, they'll often share memes, jokes, ect. that become inside jokes, blossoming into a pair of dopplegamers. Always in a pair (sometimes more) when engaged in their gamer duties.

"Those two are pretty close. They're reading each others minds and covering every flank."
"Yeah, they're dopplegamers."