Momoka Yashiro, nicknamed Momo, attends middle school with Riku Mikami and Yukio Hidaka. An assertive member of the girls' soccer club, she initially attempts to recruit Riku while embodying her personal motto: "cuteness equals righteousness." Her interests shift upon discovering Gunpla and the virtual game Gunpla Battle Nexus Online (GBN), where she transitions from soccer to building and battling alongside her friends. Her GBN debut uses a Haro-like guest avatar, followed by piloting a rented Kapool mobile suit that inspires her customized PEN-01M Momokapool.

Cheerful, kind, and perpetually seeking fun, Momo maintains unwavering positivity and fierce loyalty, readily defending her friends. Within GBN, she forges an older-sister bond with the enigmatic Sarah, patiently teaching her unfamiliar concepts and becoming a trusted confidant.

As a close-range combat specialist piloting the Momokapool, Momo adapts strategies swiftly when plans falter. She demonstrates notable synergy with Riku, executing their "Infinity Shot" combination—where Riku’s Gundam 00 Sky activates Trans-Am Infinity to accelerate her Momokapool’s Petitekapool unit. Collaborative Gunpla building sessions with Riku cement her role in the group. Momo continues her GBN adventures into the sequel series, maintaining her dynamic within the team.