Good question, short answer Mages. And 5pb

Long answer

Mages. Is the more well known of the two, as her appearance and personality, and behaviour are all based off of Steins Gate. 5pb however is the one some users may not be aware of. In some entries to the games, 5pb has direct movesets based off of Steins Gate, these include dropping a giant version of that metal gacha toy from season 1 on the enemy or hitting them with her guitar to knock them into the same microwave as the anime. 5pb was actually the company responsible for Steins Gate, but takes in most aspects her character design from other company products so the references came out in her attacks. Given the popularity of Steins Gate at the time when they decided to make 5pb's parent company MAGES. into a DLC maker for Victory they decided to make her a more direct Steins Gate reference then 5pb's attacks. This is also why these two makers are blood relatives in the games

so technically both answers work