Anko Isuna, whose true name is Acena, hails from the same otherworldly village as Twoearle. She was initially driven by a profound admiration for Twoearle, which expressed itself through a secretive fandom and persistent stalking.

When Twoearle vanished from their home dimension, Acena followed her trail to Earth. To aid her search, she infiltrated the hostile Ultimegil organization, operating under the alias Dark Grasper—sometimes translated as Dark Glassper. During her tenure with Ultimegil, she wielded a weapon called the Sickle Grave of Darkness.

After successfully locating Twoearle on Earth, her loyalties changed. She betrayed Ultimegil to side with Twoearle and the Twintail warriors. Following her defection, she adopted the identity of Tail Black, arming herself with the Darkness Grave Moebius.

On Earth, she maintains a civilian life as Anko Isuna, working as a singer—a public role separate from her other activities. Her appearance is marked by dark hair and violet eyes, with her hair typically arranged in two pairs of twintails. As Dark Grasper, she wore the Robust Armor of Glasses Element.

A key event involved Dark Grasper kissing Tail Red. This kiss deeply affected Tail Red’s civilian identity, Souji Mitsuka, gradually shifting his obsession from twintail hairstyles to an interest in the female form itself. This change temporarily impaired his ability to transform, even triggering an involuntary gender transformation that weakened his powers until he could rediscover his passion for twintails.

She is regularly accompanied by a robotic partner, Mega Neptune Mk. II, whom she calls by the nickname “Megane.”