Epic Games, makers of Fortnite, the world’s most popular game today, have been sued by the studio behind rival title, Player Unknown’s Battlegrounds (PUBG).

Fortnite and PUBG both have similar gameplay elements where they pit a large number of players in last man standing matches. The gameplay approach has become increasingly popular and has seen millions of players tuning in every day.

PUBG first soared in popularity last year when they introduced the battle royale shooter genre to players. Their success prompted Epic Games to launch their own version of battle royale in Fortnite, a game which now dominated Twitch streams to become literally the most popular game on the planet with 3.4 million people playing at one time.

The developers behind PUBG, Bluehole, a Korean company have now taken to South Korean courts to determine whether Fortnite has copied PUBG. “We have filed the suit to protect our copyright.” says an unnamed spokesperson for PUBG in a confidential statement to The Korea Times.

While it is still unclear exactly how Fortnite has infringed upon PUBG, the two games share the same Unreal Engine 4 which, ironically, was created and licensed by Epic Games. Although we are no experts in cases of intellectual copyright, going by PUBG’s approach, every other shooter game would be throwing a barrage of lawsuits at rival titles in hopes of curbing their competition.

PUBG has sold over 40 million titles since it was released has been released on Xbox One as an exclusive title. Fortnite took a different approach and chooses to be a free-to-play title, being easily available on all consoles, their popularity allowed the game to make nearly $300 million in the month of April alone.

Seeing their popularity on consoles and PC, both games decided to try mobile versions, on which they have seen similar success.

The idea behind PUBG’s last man standing approach

PUBG was released in March 2017 and was inspired by the Japanese thriller, Battle Royale, in which a group of students were forced to fight to the death by the government. PUBG took a similar approach by having 100 players parachute on an island, search for weapons and kill one another until the last player remains.

Fortnite has the same approach, having 100 players land on an island and kill each other in a last man standing battle royale. Analysts have suggested that PUBG’s popularity has fallen since January and have hopped on to Fortnite. This transition of players from PUBG to Fortnite didn’t sit too well with Bluehole who decided to take their rivals to court.

Apart from this tumultuous relationship however, the two companies have a healthy business relationship with each other. Since its launch, PUBG has made over $1.3 billion while Fortnite makes more than $200 million a month.

Despite its free-to-play approach, the game generates sales through cosmetic skins for weapons and characters which are exclusive and don’t give unfair advantages to players who don’t have them.