Mitsuko Souma was a girl with a troubled past, having been sold as a child prostitute by her own mother. Unsuprisingly, she ended up as a juvenile delinquent. Souma was a member of a class selected by the government of an alternate Japan where the fascist government persisted to the 21st century, as part of a program where a class of 9th graders were to fight each other in a "Battle Royale".
The program was presumably some sort of means to control the population through terror. Souma's past resulted in a violent personality, which thinks nothing of killing. Souma kills several people during her time in the Battle Royale, at one point distracting two male students by offering them sex, and cutting their throats. Souma is herself finally killed by Kazuo Kiriyama, a student every bit as psychotic as Souma herself, who shoots her to death with her own Colt M1911.
Battle vs. Rena Ryūgū (by SPARTAN 119)
Six months after the end of the Higurashi Kaku OVA
Rena walked into an abandoned apartment in an abandoned ten-story block on "Battleship Island", nata at he side and a rifle she took from the psychotic villagers of Hinamizawa in her hands. Rena looked out the window and spotted a girl with a handgun in one hand and a kama scythe in the other. Suddenly, the girl raised her Colt M1911 and fired three shots, which narrowly missed Rena, cracking pieces concrete off the walls.
Rena raised her rifle and took aim at her attack, fire a shot, but missing. Rena worked the bolt as quickly as possible, before firing again as Mitsuko Souma ran for the cover of the building. Rena entered the stairwell of the apartment block and fired down the gap in the staircase, missing Mitsuko yet again, who fired several times, again, all missed shots.
Rena and Mitsuko exchanged fire several times, but by the time Mitsuko was half way up the stairs, both girls were out of ammunition. Instead, Mitsuko charged up the last few flights of stairs, kama in hand, and made a wide slash at Rena's throat. Rena dodged the attack and retaliated with her nata, grazing Mitsuko's side.
Furious, Mitsuko swung the kama downwards, trying the bury the blade in Rena's skull, but Rena jumped backwards and evaded the blow... but landed on a metal pipe lying on the ground, causing her trip on the pipe and fall on her back, dropping her nata in the process.
Mitsuko pressed her advantage, standing over Rena with her with her scythe at the ready. Rena grabbed the metal pipe on the floor and raised it in front of her, blocking the strike. Rena then got up and swung her pipe at Mitsuko, striking her in the jaw, breaking the bone and causing her to spit up blood. Rena the struck Mitsuko again, knocking her to the floor.
Rena retrieved her nata and stood over the wounded Mitsuko.
"If you want to kill someone....", Rena said darkly as she raised her nata, "You should be prepared to die yourself!"
Rena brought down the nata on Mitsuko's head, releasing a spray of blood as the blade practically split her skull. Rena pulled her blood-stained blade out of Mitsuko and walked away from the scene of carnage.
WINNER: Rena Ryuguu
Rena won this battle because of her dominance of most of the X-Factors, particularly combat experience and physical strength. Her superior weapons also contributed to her victory.