Īsuna, operating under the alias Anko Īsuna and the codename Dark Grasper, hails from a parallel dimension linked to the antagonistic Ultimegill organization. Tasked with infiltrating Earth as Dark Grasper, her covert allegiance to her homeworld’s figure Twoearle compels her to defect from Ultimegill upon their reunion, realigning with the protagonists.

In her initial role, she wields the Sickle Grave of Darkness, later adopting the Tail Black identity post-defection to deploy the Darkness Grave Moebius—a weapon system synergized with detachable armor components. These modular pieces reconfigure into autonomous combat units, enabling adaptive battlefield strategies.

Her arc intertwines antagonism with clandestine devotion to Twoearle, whom she obsessively tracks across realities. This fixation catalyzes her betrayal of Ultimegill and pivotal actions, such as triggering a kiss with Tail Red that fractures the protagonist’s twintail-based power linkage, inducing temporary loss of abilities and gender identity turmoil.

Undercover as idol Anko Īsuna, she conducts operations alongside the robotic aide Mega Neptune Mk. II (“Megane”), whose tactical algorithms clash with her improvisational methods despite their operational synergy.

Chronicled across light novels and anime, her narrative spans redemption, the integration of masochistic combat traits, and eventual acceptance among protagonists through joint campaigns against Ultimegill’s forces.