Mega Neptune Mk. II, a towering mechanical ally crafted by Anko Īsuna, operates initially as her trusted counterpart within the Ultimegill syndicate. Its formal designation is frequently shortened to "Megane"—a nickname it pointedly rejects—due to the impractical length of its full title. The machine’s 1.99-meter frame and 481-kilogram build grant it an imposing stature that contrasts with its supportive role as Anko’s strategist and aide.

Following Anko’s defection from Ultimegill to join the Twintail Warriors, the robot assumes the mantle of Tail Silver, repurposing its advanced systems for frontline combat. This rebranding marks its evolution from an asset of antagonistic operations to a defender of Earth against alien incursions. Equipped with cutting-edge combat systems, Tail Silver provides tactical support in battles, though precise technical specifications of its arsenal remain undisclosed.

The robot sustains an unwavering partnership with Anko, balancing battlefield utility with steadfast loyalty. Its adaptability proves critical in bridging alliances with former rivals, navigating shifting allegiances without compromising its core function as her confidant and tactical enabler. Interactions underscore a dynamic defined by mutual reliance and strategic precision, anchoring its presence within the team’s collaborative efforts.