Aquos Sirenoid originates as a mermaid-like Bakugan wielding a magical lyre designed to soothe souls with music and generate forceful combat waves. Her physical form features a dolphin-like tail for aquatic mobility and protective flowing robes. As the dedicated Guardian Bakugan of Klaus Von Hertzon, she shares an exceptionally close bond with him, displaying deep loyalty and affection. This connection includes residing in a fish tank within Klaus's Vestal office, reflecting her Aquos attribute. In *Battle Brawlers*, her personality shifts under external influences. Initially calm and strategic, she adopts a vicious demeanor when corrupted by the Silent Core's negative energy. During battles, she demonstrates tactical prowess through abilities like "Anthemusa" to lure opponents and "Dive Mirage" for repositioning. Her conflicts involve sending Preyas to a negative energy zone, battling alongside Fourtress and Tentaclear against Drago's team, and contributing to Griffon's banishment to the Doom Dimension. After Klaus loses to Masquerade, she defies his retreat order, leading to her defeat and consignment to the Doom Dimension by Dual Hydranoid. Retrieved by the Legendary Soldiers of Vestroia, she returns to Klaus but harbors intense resentment toward Alice Gehabich as Masquerade's host. This fuels vengeful actions like labeling Alice a "coward" during their brawl, though she later assists Alice against Rabeeder. Her post-Doom Dimension experiences include aiding Klaus in motivating Alice during battle and participating in pivotal conflicts against Doom Beings Hairadee and Druman. Initially overpowered, she later helps the Battle Brawlers halt Rabeeder's threat. Her final act in this arc involves joining other Bakugan to stabilize Vestroia before returning there. In *New Vestroia*, her role transitions to support. Freed after the Vexos' initial Bakugan capture, she rejoins Klaus on Vestal, adopting a calmer disposition. She frequently plays her harp while observing the Resistance and serves as Klaus's secretary, managing his schedule and communications. In combat, she aids Ace Grit against Mylene Farrow using abilities like "Devora Anthemusa" to nullify opponents and "Ripple Shield" to weaken them. Her bond with Klaus remains central, highlighted by bashful reactions to his praise. She continues residing in a fishbowl in his Vestal office. Her abilities evolve across media. *Battle Brawlers* techniques include "Forcing Wave" (adding 100 Gs) and "Anthemusa" (relocating opponents). The video game iteration enhances "Forcing Wave" to 200 Gs. *New Vestroia* introduces upgraded powers like "Vital Neptune" (nullifying abilities while adding 200 Gs) and "Devora Anthemusa" (nullifying abilities while adding 300 Gs), reflecting adaptability in newer brawling systems. Her name derives from Greek mythology's Sirens, reflecting her mermaid motif and enchanting musical traits. Her Japanese name, "Siren," further emphasizes this connection.