Lena Isis is an Aquos-attribute Bakugan brawler from Gundalia. She operates as a tactician within the Gundalian Agents, a subgroup of the Twelve Orders serving Emperor Barodius. Her partner Bakugan is Phosphos, and she employs the Battle Gear Terrorcrest. She has blue hair usually in a bun and wears distinctive Quevedo-style glasses, less prominent in her true Gundalian form.

Initially fiercely loyal to Gundalia, Lena infiltrates the virtual Bakugan Interspace under Ren Krawler. Her missions involve strategically recruiting powerful brawlers, often partnering with Sid Arkale and Zenet Surrow. During a mission with Sid, she defeats Marucho Marukura's Akwimos but loses to Dan Kuso's enhanced Drago. Later, she assists Mason Brown in deliberately losing battles to lure recruits, delivering hypnotized victims to Kazarina and Barodius. Lena maintains a quiet demeanor outside battle but exhibits tactical arrogance during brawls, appearing less aggressive than Sid. She shows concern for fellow agents, particularly Sid's well-being, and maintains a close friendship with Zenet Surrow, the only other female Gundalian Agent.

A critical turning point follows Lena's repeated mission failures. After Shun Kazami defeats her during an attempt to stop Neathia's second shield activation, Kazarina punishes her for both the failure and attempted insubordination – Lena had ordered Phosphos to ambush Kazarina over prior threats. This results in her apparent disposal, though she is later discovered alive alongside Jesse Glenn and Zenet Surrow, confined in stasis tubes within Kazarina's lab. During captivity, Kazarina places Lena under hypnosis, forcing her to battle Neathian forces like Fabia Sheen and Nurzak.

Lena's allegiance shifts permanently after Kazarina's demise. Freed from hypnosis with Jesse and Zenet, she volunteers to aid the Neathian resistance against Barodius, an offer accepted by Captain Elright. She fights in the Neathian-Gundalian War's final battles alongside former enemies to protect Neathia. In the conflict, she witnesses Phosphos defeated by Phantom Dharak during an attack attempt. She later reunites with Mason Brown and Nurzak, expressing visible shock at Mason's survival. Post-war, Lena returns to Gundalia with Ren, Mason, Zenet, Jesse, and Nurzak, contributing to establishing a new government and peaceful relations with Neathia. Her battle record shows four wins, though she is noted as the only Gundalian Agent without a solo match victory.

Lena's development includes a nuanced relationship with Mason Brown, hinted by her visible concern and physical reactions upon their reunion. Her strategic intellect and bond with Phosphos remain consistent traits throughout her journey, from loyal Gundalian operative to allied force member working for interplanetary peace.