Attribute: Aquos
Guardian Bakugan: Preyas, Elfin (Dual Elfin), Angelo/Diablo, Akwimos, Tristar
11(Bakugan),and believed to now be about 14
For an eleven year old, Marucho is wise beyond his years. Studious, he studies the strategy of Bakugan as well as being a bit of a walking encyclopedia. Marucho is the only son of a millionaire. In the Bakugan battles, Marucho devises strategy based on in-depth data analysis but sometimes misjudges his spur-of -the-moment decisions based only on data. As a sidekick to Dan, Marucho helps work out which Bakugan would be best to pit against one’s opponent. He worries about all of the Brawlers, but especially Dan. Marucho is a master of combination play, and uses water attributes in battle.

He is a wealthy, generous boy who specializes in Aquos. He is the brain of the Brawlers, a real walking encyclopedia. He loves to play Bakugan and work on strategies. He use to be extremely obedient to his parents out of fear, but that changed when he joined the Brawlers, however he is still very obedient. He now has no regrets for the past, realizing that he only wanted to make his parents happy. Marucho has a butler named Kato.

His Guardian Bakugan is Aquos Preyas, which he obtains when Preyas crashes his house party, which was thrown after he moved into Dan's town. Preyas was sent to the Doom Dimension in Marucho's battle with Klaus Von Hertzon which made Marucho want Preyas back so much that when Klaus opened up his portal, Marucho followed him. Later, when Klaus shows up with Preyas Dan and Runo find a way to get Preyas back by using the ability Pure Light. Preyas evolved into a two-sided Bakugan called Angelo and Diablo by coughing them up. Unlike the other Bakugan however, Preyas multiplies when he evolves, so Marucho got to keep the old Preyas. He multiplied into Angelo/Diablo Preyas. Preyas also has a move called "Change of Attribute" with which he can take advantage of the opponent’s gate card. When Marucho was being tested by Frosch he had to fight an old version of himself, the one who always listened to his parents. This sickened him but he was able to accept his past and how it made him who he is today and passes the test. When he brawled against Dan with Preyas and Angelo/Diablo Preyas he was ranked seventh. Preyas Angelo/Diablo are not in New Vestroia.

Marucho returns in New Vestroia, following Dan and Drago into the new world. When the Vexos attack first against Dan and Mira, he stands back and observes the new way of battling.

Marucho later goes to the Resistance headquarters and gains new clothes. By episode 4, Marucho is disappointed with himself, as he is part of the Resistance, yet doesn't have an Aquos Bakugan (Either Mira, Baron, and Ace weren't able to catch one or lost the ones they had) (in the English version they say they don't have any Pyrus Bakugan). Marucho decides to leave for a bit so that he can look for one.

While walking through a jungle, he is caught in a trap set up by a Bakugan called Elfin, who resembles Sailor Moon. Elfin gives him some food while she explains about how she knew Preyas before he got captured. Marucho than decides that they should team up, but Elfin wants Marucho to prove himself that he's really the "right partner" for her.

Bakugan: Gundalian Invaders:
Added by TwinStarHe is the most intelligent of the brawlers and has a new outfit in Gundalian Invaders. His new Guardian Bakugan will be Akwimos. After Ren gave him a new Phantom Data, Marucho created Bakugan Interspace which allowed all brawlers around the world to battle each other.

In episode 1 it is revealed that Marucho has Aquos Trister from Gundalia. Also, he turned over administrative duties of Bakugan Interspace to the system, allowing it to expand but also attracting sleazy characters such as a card dealer named Dylan. He observes Dan's battle against Ben but then sends out Trister to stabilize the arena when Drago loses control of his powers.

In episode 2, he is seen battling Jack Punt, a member of Team Anubias. At first, he and Trister were struggling but were starting to come back before Zenthon appeared. They tried battling him but Trister was defeated by Zenthon's laser blast. The battle was declared a draw due to Zenthon's interference. He comments later "that Mechtogan has the same destructive power as Drago".