Yoko Littner hails from Littner Village, where she honed combat skills defending her community against Beastmen and their Gunmen. Her path intersects with Simon and Kamina during a pursuit of a Gunmen breaching Giha Village's ceiling, leading her to join their quest to reach the surface and overthrow the Spiral King. She serves as the team's sharpshooter, wielding specialized firearms such as a uranium-bullet rifle effective against Gunmen armor, complemented by handguns for close combat. Her exceptional marksmanship enables feats like disarming adversaries using human shields and destroying multiple Gunmen single-handedly.

Initially defined by practicality and rationality, Yoko provides grounded perspectives within Team Dai-Gurren. She forms a romantic attachment to Kamina, sharing a pivotal kiss before his death—an event that profoundly shapes her. In the aftermath, she builds a sisterly bond with Simon, supporting his leadership while processing her grief. Her initial distrust of Nia, stemming from Nia's lineage as Lordgenome's daughter, transforms into mutual respect and friendship forged through shared battle.

Seven years post-timeskip following Lordgenome's defeat, Yoko adopts the alias "Yomako" and becomes an elementary school teacher on Koreha Island, rejecting violence and political involvement in Kamina City. Her philosophy shifts toward nurturing future generations, emphasizing non-violence to her students. When Beastmen attack the island during the Anti-Spiral crisis, she temporarily resumes combat, utilizing her rifle before piloting mecha such as the Space Dayakkaiser and Yoko M Tank. She participates in critical battles against the Anti-Spirals, including operations to destroy the Death Spiral Machine. Her interactions with Kittan involve unspoken mutual respect, culminating in her accepting his farewell kiss without protest before his sacrificial act.

Within the Anti-Spiral's multiverse labyrinth, Yoko witnesses alternate life possibilities—including roles as a bounty hunter, model, or Kittan's wife—yet affirms her chosen path. Her final actions include supporting Simon's wedding to Nia and returning Nia's ring to him after Nia's disappearance. Decades later, she serves as principal of the same island school, continuing her commitment to education.

Her mechanical involvement extends to piloting the Yoko M Tank, featuring spiral-powered barriers during the Anti-Spiral War, and integrating into larger collective mecha like Tengen Toppa Gurren Lagann. Spiral Power fuels her combat effectiveness, though its potency wanes if her resolve falters.