Pandora in the Crimson Shell: Ghost Urn Vol. 6 (manga)

The massive multi-legged boring machine Buer is now deep underground, but that doesn't stop the American Empire from trying to retrieve it and throwing Centacle Island into chaos. Clarion infiltrates the Empire's secret base, hoping to assist Nene--only to find herself face to face with a combat android! After Clarion vanishes, Nene goes to seek her in the underground base--accompanied by Buer's erratic central nervous unit.