Marucho Marukura, nicknamed Marucho, hails from immense wealth as an only son. Initially paralyzed by obedience due to fear of parental disapproval, joining the Battle Brawlers sparked a transformation. While maintaining respect, he gained independence, understanding his past compliance stemmed from a desire to please, not weakness. He serves as the Battle Brawlers' strategic core, celebrated for his analytical brilliance and encyclopedic grasp of Bakugan mechanics. An Aquos specialist, he excels at crafting complex battle strategies, though spontaneous decisions sometimes reveal an over-reliance on data. His signature combat style involves mastering combination attacks and exploiting the fluid nature of water-based abilities. His initial Guardian Bakugan is Preyas, an Aquos Bakugan with shifting attributes. Preyas faces banishment to the Doom Dimension during a clash with Klaus Von Hertzon. Driven by resolve, Marucho plunges after Klaus through a portal. Dan and Runo later secure Preyas's return using the Pure Light ability card. Preyas then evolves, splitting into Angelo and Diablo Preyas, while the original Preyas remains with Marucho. In the New Vestroia conflict, Marucho secretly follows Dan and Drago to aid the Bakugan. Feeling powerless without an Aquos partner after Preyas's capture by the Vestals, he journeys into the wilderness. There, he encounters Elfin, a Bakugan trained by Preyas. Proving himself by teaming with Elfin to defend Aquos Bakugan, especially Wontu, against the Vexos member Mylene Farrow—a battle where Shun Kazami intervenes to prevent defeat—Elfin agrees to become his new Guardian. Marucho and Elfin achieve key victories, including defeating Shadow Prove to reopen a dimensional portal. However, Volt Luster captures Marucho before Mira Fermin and Spectra Phantom rescue him. He later participates in critical missions: battling in Gamma City to let Dan and Ace destroy a Dimension Controller, and aiding in liberating petrified Bakugan, including Preyas, from Prince Hydron's palace. Preyas's return sparks rivalry between him and Elfin for primary partnership, though they eventually cooperate. Elfin evolves into Minx Elfin after receiving energy from the Six Ancient Warriors. Providing sanctuary on Earth, Marucho shelters the Resistance within his shielded mansion to evade Vexos detection. Despite later defeating Shadow Prove and Hydron, Elfin loses her Aquos Attribute Energy. He and Ace then fall to Shadow Prove and Lync Volan due to a Trap Field, resulting in the loss of the Darkus Energy. Collaborating with Keith, Marucho develops the JetKor Battle Gear for Drago. Following the defeat of the Alternative weapon system, Akwimos becomes his new primary Guardian Bakugan entering the Gundalian Invaders conflict. During Gundalian Invaders, Marucho demonstrates heightened intellect and technological skill. Using Phantom Data from Ren, he creates Bakugan Interspace, a global battling network, initially ranking third within it. His strategic acumen impresses Queen Serena of Neathia, earning recognition for devising effective decoy operations. He faces profound personal challenge when betrayed by Ren, struggling with his deception during their battle. Yet, Marucho maintains belief in Ren's underlying loyalty, ultimately vindicated. He later battles Jake while disguised and contributes to the final confrontations against Gundalian forces. In Mechtanium Surge, Marucho initially partners with Infinity Trister, later bonding with Radizen and temporarily Roxtor. Radizen exhibits a talkative, humorous personality echoing Preyas. Preyas, residing on New Vestroia, trains Bakugan like Amazon and aids in defending the planet against the Mechtogan threat, ultimately perishing in a dark future timeline before the event is reversed via the Current of Time. Throughout his journey, Marucho evolves from a compliant child into a resilient strategist and loyal comrade, consistently leveraging his intellect and resources to protect both human and Bakugan worlds alongside his partners.