Mysterious cards appear in front of the children of the world, with the powers to summon monsters from an alternate dimension. When card-fighting group Battle Brothers Dan unleashes the power of Drago card in battle, he's sucked into an alrernate dimension causing a break in the balance of both worlds and possibilty the end to all humanity.
* Daniel "Dan" Kuso: Dan is a boy who loves playing Bakugan and gets frustrated easily. His greatest ambition is to be the number one battle brawler in the world. He is a Pyrus battler, and his guardian Bakugan is a Pyrus-attribute Dragonoid (nicknamed Drago). His Drago loves Wavern/Wayvern, who holds the Infinity Core within her. Dan and Runo often argue with each other; Dan is in love with Runo but doesn't confess until the end of the series, when they are seen on a date together. In the anime television series, Dan is voiced by Yu Kobayashi in the Japanese language and Scott McCord in the English language. Drago is voiced by Keiji Fujiwara in the Japanese language and Jason Deline in the English language.
* Runo Misaki: Runo is a tomboy who loves playing Bakugan with people that have skills to show off. Runo is a Haos battler. Her Guardian Bakugan is a Haos-attribute Tigrerra, who is very obedient to her and powerful in battle. Runo hates when people think that they can beat her just because she is a girl. She helps her parents run their family business. When Alice comes to visit, she helps Runo's family with their restaurant, which leads to Runo becoming jealous as boys came just to see her. At the end of the series she and Dan are seen on a movie date. In the anime television series, Runo is voiced by Eri Sendai in the Japanese language and Julie Lemieux in the English language. Tigrerra is voiced by Atsushi Ono in the Japanese language and Stevie Vallance in the English language.
* Marucho Marukuro: He is a extremely wealthy boy who is very generous and smart, a bit like a walking encyclopedia. He loves to play Bakugan and he also likes to work on strategies. He used to be very obedient to his parents just because he wanted to please them, but that changed when he met the Brawlers. He now has no regrets for the past, realizing that he only wanted to make his parents happy. He is an Aquos battler. His Guardian Bakugan are an Aquos-attribute Preyas and a Haos Angelo/Pyrus Diablo Preyas(showing up later in the series). Preyas was sent to the Doom Dimension in Marucho's battle with Klaus Von Hertzon. Later Klaus shows up with Preyas. Dan and Runo find a way to get Preyas back through defeating him in battle. Preyas evolves into a two-sided Bakugan called Preyas Angelo (Haos) and Preyas Diablo (Pyrus). Unlike the other Bakugan however, Preyas multiplies when he evolves, so Marucho got to keep the old Preyas. Preyas also has a move called "Change of Attribute" with that he can take advantage of the opponent's gate card. In the anime television series, Marucho is voiced by Ryou Hirohashi in the Japanese language and Joanne Vannicola in the English language. Preyas is voiced by Shawn Unifier.
* Julie Makimoto: Julie is a girl who tries to stay happy even when the worst has happened (for example, when Billy ended up under the control of Masquerade); her acting happy after something terrible happened is generally just to cover up her real feelings. Julie forgets things easily, proving that she is a little scatterbrained at times. She is a Subterra battler, whose guardian Bakugan is a Subterra-attribute Gorem. At the beginning of the series, she is shown to have a little crush on Dan (which led to some arguments with a jealous Runo), but later, accepts that Dan and Runo are going out. At the end, she and Billy go on their first date. Julie has a sister named Daisy who has bested her in everything since she was a child. In the anime television series, Julie is voiced by Risa Mizuno in the Japanese language and Katie Griffin in the English language. Gorem is voiced by Hiroki Yasumoto.
* Shun Kazami: Shun is a boy who is the former first ranked Bakugan player who later moves down to sixth position. He is a master of Bakugan, and is also Dan's childhood friend. Shun is a loner, a boy of very few words, yet is willing to help his friends at every turn almost. He is a Ventus battler. He approaches Bakugan like a ninja. He lives with his grandfather (who used to be a famous ninja warrior) who once expected Shun to follow in his footsteps instead of playing Bakugan. His Guardian Bakugan is a Ventus-attribute Skyress whom Shun received from his comatose mother in the hospital. Shun once leaves the brawlers when Dan says they don't need him. But after brawling Komba, Dan appears and asks for forgivness which Shun accepts. In the anime television series, Shun is voiced by Chihiro Suzuki in the Japanese language and Zachary Bennett in the English language. Skyress is voiced by Chiharu Suzuka.
* Alice Gehabich: She is a girl from Moscow. She sometimes plays Bakugan because she has the evil darkus in her control, but knows almost everything about it. Michael Gehabich is her grandfather, but after learning that her grandfather became Hal-G and works with Naga, she constantly worried about him. Alice usually just gives advice to the brawlers, instead of battling. Alice and Marucho are the 2 brawlers who mostly use strategy. However, unlike Marucho, Alice gives her strategies to the brawlers. During season 2 she left the Brawlers after finding out that she was Masquerade out of intense guilt over what she did as him, but later returns as Masquerade in time to save Dan and Drago. Once she saves them Masquerade permanently leaves her body (which Alice at first resents because she believed that she needs him), but leaves Alpha Hydranoid for her to control, although her secret Bakugan is Darkus, which she hardly uses it because of its evil. In the anime television series, Alice is voiced by Mamiko Noto in the Japanese language and Emilie Barlow in the English language.
* Masquerade: He used to be the first-ranked Bakugan player before he left Alice's body. His goal is to send all Bakugan to the Doom Dimension with his Doom Card, so he can evolve his Hydranoid and have the ultimate Bakugan. He is a Darkus battler. He is revealed to be Alice in episode 38 and his origin is revealed in episode 39. Masquerade came to life when negative energy changed Alice (who doesn't know she is Masquerade or what happens when she becomes him). Darkus Hydranoid is Masquerade's guardian Bakugan. He battles with Dan in episode 38 and loses. He is actually Alice, but Masquerade disappears from her body (although at first, Alice doesn't want him to leave). In the anime television series, Masquerade is voiced by Souichiro Hoshi in the Japanese language and Lyon Smith in the English language.
* Joe Brown: Also known as Webmaster Joe. He lived in a hospital. The Brawlers used to think he was working for Masquerade, but he actually sent a message to the Brawlers to warn them that Masquerade was plotting against them. When he met Dan, he said he would only tell him if he was working for Masquerade if Dan beat him in a battle. In the middle of the battle he fainted. When he woke up they asked him to be one of the Brawlers. He gladly accepted. Sometime after he moved to the Brawlers neighborhood, he found Wavern/Wayvern who had the Infinity Core inside her. Wavern/Wayvern is a White One, meaning she has no attribute, but her abilities in battle are considered Haos. Wavern/ Wayvern is Joe's guardian Bakugan. It is also revealed that Wavern/Wayvern is Naga's younger twin sister. Joe is the first person to beat Masquerade at Bakugan with his new Bakugan Wavern/Wayvern. In the anime television series, Joe is voiced by Souichiro Hoshi.
* Billy Gilbert: Julie's childhood friend and 10th Ranked Bakugan Player. He defeated Julie when they first battled, but lost in a rematch, and lost 2 more times when he was under the control of Masquerade.Once while batteling under Masquerade's rule Billy almost sends both Gorem and Julie to the doom dimension. He is shown to like Julie in episode 47, "Here's mud in your eye" or in the Japanese version, "Good night baby". At the end of the series Julie asks him if he would like to go on a date some time, and he agreed. Also, at the end of episode 47 Julie makes it known that the two are boyfriend and girlfriend. It is assumed that they are still going out.
* Klaus Von Hertzon: He was once the second ranked Bakugan player, but later moves down to rank 4 after being defeated by Masquerade. He is an Aquos battler and his guardian Bakugan is Aquos Sirenoid. He is the guy who sent Marocho's Aquos Preyas into the Doom Dimension. He somewhat has a crush on Alice.
* Chan Lee: The third rank brawler that appeared in episode 14, and was recruited by Masquerade. She uses Pyrus attribute Bakugan and her guardian Bakugan is Pyrus Fortress. Dan Kuso beat her on episode 16. Pyrus Fortress gets sent to the Doom Dimension in Episode 26. She is reunited with him sometime around episodes 32 and 36. She has a crush on Joe and at the end of the second series when Dan is on his date with Runo, she and Joe can be seen together in the background. In episode 49 Chan rescues Joe from Hal-G using her martial arts moves. She is voiced by Candi Milo
* Komba O'Charlie: The 5th Ranked Bakugan player and Julie's neighbor. He uses Ventus attribute Bakugan, Harpus. He used to be rather selfish and refused to accept his first defeat from Shun and challenges him again, although he lost. He was ranked fifth best Bakugan player until his defeat in episode 26 and the loss of Harpus, which was Masquerade's doing.
* Julio Santana: The 4th Ranked Bakugan player and self-proclaimed master of Haos-attribute bakugan. His Guardian Bakugan is Haos Tentaclear.Tentaclear does not talk but is strong in battle.