Proto is a bioroid member of Public Security Section 9 introduced during the second season. As a biological android, Proto possesses a body incorporating organic elements, though the extent and nature of these biological components are not detailed. Initially serving as the maintenance technician for the Tachikoma think tanks, he manages their upkeep and operational support. His designation as a "prototype" signifies his experimental status within the unit.

Proto's responsibilities extend beyond technical duties to include functioning as Chief Daisuke Aramaki’s chauffeur and de facto bodyguard. During the Dejima crisis—involving a refugee uprising and governmental coup—Proto plays a critical role in Aramaki’s efforts to rescue Prime Minister Yoko Kayabuki from house arrest. He accesses the network to communicate with the Tachikoma units, retrieving building blueprints and real-time operational intelligence for Section 9’s mission. This enables the team to locate the Prime Minister before an attack barrier incapacitates Proto.

The character reappears in the film *Solid State Society*, set two years after the Dejima incident. Proto is depicted wearing Section 9’s standard black uniform and carrying a sidearm, indicating a transition to field operations and formalized combat duties. Discussions among fans and analysts speculate whether Proto possesses a "ghost"—denoting consciousness in the series' lore. Arguments draw parallels to the Tachikomas, which developed self-awareness without biological brains, though no definitive confirmation exists within official media. Proto’s origins trace back to the manga *Ghost in the Shell 1.5: Human-Error Processor*, where he features as a recurring figure.