They are the three duelists who take control of all card shops in town. They also steel cards from those who lose to them and force shops to give them their money.
See: Masumi Momono
This guy has a light colored, bowl-cut hair style and is shorter than the other two. He is also fairly large and wears the most (presumably) red colored clothing of the three. During the Kame Game Shop Duelist Level Certification Tournament, he is pitted against Katsuya Jonouchi and easily defeats him with the "anti" deck Masumi gave him. Jonouchi says that his deck was poison to his own. When Yugi Mutou arrives on the seen and denounces the three as the Store Breakers, he tries to deny it but is over-shadowed by Masumi.
The third guy has darker hair than the other two and is the tallest of all three. He wears the most (presumably) white out of them and is fairly lank. His role is almost non-existent as he has no dialogue.