Camille, the Arcade Witch, or Fighting Witch. She has a challenging nature, and assumes the form of an arcade machine. Her moves include ramming into her opponents, leaping into the air to crush them, or swinging her plug cable to tie them up, strangle them, or stab them with the plug itself.
Her barrier resembles an arcade, complete with other arcade games, pachinko machines, prize grab machines, games of chance, and other manner of games. At least one survivor had described a game consisting of various fellow Witches' Barriers, where players can choose one of five different Puellae Magi to take on each Witch and her Familiars.
Her Familiars, Ryan and Kenneth, serve to challenge anyone who enters her domain to see who is worthy to fight the Witch herself. They sport white and red karate uniforms, and attack with ki blasts, uppercuts, and spinning mid-air kicks. The Witch remains dormant most of the time, and will only reveal herself to those who can defeat them.
Here is Ko, the first manga-exclusive character to gain an entry. As you can probably figure out by now, the names come from Cammy, Ryu, and Ken from the Street Fighter franchise. Also, the game described is not an actual arcade game; it's exclusive to Windows.