Taira no Tomoshige

Uses a specific symbol as its target, and kills those who carry that symbol within the area specified by the user by cleaving them in two. Its effective range is several hundred meters.

Taira no Tomoshige himself, naturally wielding the curse. A curse stone with this curse was conferred to Kikuko Tsutsui.

Taira no Tomoshige was born as the son of Taira no Kiyomori's younger brother, Yorimori, in the latter half of the Heian period at the height of the Taira clan's power. Although his father Yorimori was the only child born of the official wife of Taira no Tadamori —part of the main lineage of the Taira clan— he maintained a deferential attitude towards Kiyomori, a stance that made Tomoshige regard him with contempt and fueled his ambition to one day stand at the head of the Taira clan.
* * *
In 1185, the Taira clan was defeated at the Battle of Dan-no-ura, spelling its ruin. Tomoshige, who had fled from place to place as if to desperately avert his eyes from the Taira clan's decline, ultimately did not participate in the decisive battle at Dan-no-ura, and came to know of the Taira clan's downfall while he was lying low in a remote village in Ise with the imperial maidservant Sato.
* * *
Tomoshige continued to search for a way to turn the situation to his advantage. In the process, he suddenly remembered a box that his grandfather Tadamori had left the family — a tamatebako proffered by a fisherman that was said to contain the flesh of a mermaid.
Tomoshige located the tamatebako and pried open the lid. However, all that was inside was a dried sliver of meat, so shriveled as to resemble a splint of wood. Dubios, Tomoshige pushed his misgivings aside and ate the meat, but felt no different than before. Believing that long years had robbed the meat of its power, and seeing the tamatebako as his only clue to find a mermaid, he boarded a small boat with Sato and set out to sea.
* * *
Their small boat was surrounded by ships belonging to a small band hunting down remnants of the Taira clan. Alarmed, they tried to flee, but with their attackers pressing in on them from all sides, were unable to find any means of escape.
Tomoshige, still determined to retaliate, continued to frantically resist with his sword. However, he was vastly outnumbered, and, unable to break through his attackers' ranks, was ultimately cut down in a single stroke.
On the brink of death, Tomoshige's gaze fell on the crests worn by his pursuers. Consumed by bitter regret at his failure to restore his clan, he directed the full brunt of his resentment towards these symbols as he sank beneath the waves, cursing his enemies and clinging to his vindictive hatred until the very end.

In truth, Tomoshige successfully gained immortal and survived the attack. He lives in the modern age under the name Kippei Ikoma.
* * *
Tomoshige had spent the past 800 years working alone in the shadows, possessed by the single desire of restoring the Heike. His plan has remained unchanged: obtain wealth and status, gain the power of immortality, build up an immortal army, and rise to power through force.
He perhaps came closest to this goal during the Sengoku era, where —as Komatsu Sadamune, a vassal of the Kuki clan— he managed to invade Taishima, an island said to be the dwelling place of mermaids, but this attempt ultimately ended in failure. Refusing to give up, he continued to devise various schemes after that in pursuit of his goal, but none of them met with success.
As the modern age approached, his accumulated resentment eventually grew so strong that he gained the ability to wield it as a curse. Since attaining his power, he has sought out young men with no family of a similar age to him and used it to kill them without leaving any evidence, before going on to assume their identity. He disposed of all their bodies at a. point in the sea near Toba where the currents happened to stagnate — the perfect spot to ensure they would remain undiscovered.