That is a cool story concept.
And Kobra is also a fitting name to the snake based game title.
But if there are two sides of the tournament, wouldn't it make they can't fight their own group?
Well, in most fighting games you can pit friend against friend. And sometimes in stories one guy encounters another, don't like the cut of their jib, fight it out and become friends afterwards so there's that.
Kobra users in mind are
Jane who is perhaps strong without the drug, but took it anyway during her application for the Marines and was disgraced for it.
Raxel who is a wannabe punk rockstar. And as we all know, or more "who knows", what they put in themselves on a weekly basis.
Tokio is perhaps a "maybe". He left his family of Kabuki actors to join a criminal gang and eventually became the leader, so being crime and all drugs maybe involved.
Mahler, who is the one who created the drug and is using the tournament as a front to peddle it.
Charlie is a maybe who perhaps mostly uses it to enhance his BMX skills, and takes up fighting in the tournament to proove his skills.
Tokio and Charlie are the sorts I can imagine eventually switching sides. Tokio was leader of the criminal gang Black Thunder but quit when one of the members died, so maybe he has some morality over what he's doing as a criminal and may not like what kobra is doing for others. Charlie has a rivalry with Picky, I dunno how aggressive that rivalry is. But he was raised by his sister at the church so either he will realise taking kobra is wrong, or maybe he'll never do that stuff to begin with.
Probably other fighters that can be on the Kobras but I don't know which ones. But I figure can be an equal number of Kobras and Vipers.