Mukuro was born as the older fraternal twin sister of Junko Enoshima. Since their very early childhood, Junko influenced and manipulated Mukuro into working towards Junko's desire to "paint the world in despair" and planned to start The Tragedy, which Mukuro was happy to support her. At some point Junko adopted the moniker "The Despair Sisters" for the both of them. When prompted, Mukuro alludes to her early life of being "on the streets" and like a "war zone"; however, due to conflicting stories and Mukuro was impersonating her twin at the time, it is unknown if it is intended to be taken literally or figuratively. At some point prior to becoming a teenager, Mukuro disappeared while she and her family were on vacation in Europe where she joined the elite mercenary group based out of the Middle East named Fenrir Mercenary Group, who engaged in direct combat. During her time spent in the group, she never received a single injury on the battlefield, and received a wolf tattoo as all members of the Group were required to have. She also travelled to at least one other country during her time spent in the Group: Southeast Asia. Some years after, Mukuro was called back to Japan by her sister to continue with their plan prior to enrolling in Hope's Peak Academy. It is unknown what Mukuro's previous high school was as she was outside the country, but she was still eventually scouted to be a part of Class 78th as the Ultimate Soldier alongside Junko as the Ultimate Fashionista. To ensure that Mukuro's skills were still useful to her, Junko ordered her to slaughter an entire middle school using only her knife. This event was later dubbed the Giboura Massacre, with only two survivors: best friends Takumi Hijirihara and Shūji Fujigawa. This event had far-reaching consquences several years after Mukuro's death such as Takumi becoming the infamous Killer Killer and a group of unknown women to worship Mukuro to the degree of emulating her appearance and killer nature. On Junko's orders, she aided her sister in tracking down and discovering where Izuru Kamukura was after dispatching several security personnel. While Junko is delighted to see Izuru, Mukuro is concerned for her safety. She attempted to attack Izuru after he stomped on Junko, but was easily overpowered by being backhanded into a wall. Mukuro recovered as Junko gives Izuru her speech, though he knocked her unconscious, Upon Junko waking up in the infirmary after being brought there by her sister, Mukuro dutifully delivered the message from Izuru. Both Junko and Mukuro carried out and succeed in setting up the very first Mutual Killing Game: The Tragedy of Hope's Peak Academy involving the Student Council. She callously shot one of the members after she resisted, afterwards joined her sister in watching the carnage unfold on several TV monitors. Junko also, pushed her to perform Tsubasa o Kudasai during it. Mukuro further aided Junko by threatening Ryota to use the footage of the massacre to create the first Despair Video, kidnapped Mikan Tsumiki after she was caught trying to check on Ryota, fighting off Peko Pekoyama, lobotomizing Chisa Yukizome, and eventually aided Yasuke Matsuda in developing further brainwashing methods. While Junko was under the effects of Yasuke's memory-erasing technology and living as Ryoko Otonashi, Mukuro donned her Junko disguise for the very first time and masqueraded as her. During this period, she murdered two members of The Steering Committee and all the The Madarai Brothers in either hand-to-hand combat or traps. Following the events after Junko recovered her memories, she and Mukuro further solidified the Mutual Killing by preparing the Class Trial room below the school and pretended to befriend their classmates over their year of peace. They both used the information gained from their classmates to set-up the Motives and locked all of their loved ones, like Komaru Naegi, in apartments in Towa City for around a six month period. Together they also witnessed the Reserve Course students commit suicide on Junko's command. During the Tragedy, Jin Kirigiri, the Headmaster of Hope's Peak Academy, planned to seal the school building and let the students live forever inside the Academy in order to protect them from the destruction. The class agreed to his plan, and they sealed the building together. The students lived peacefully inside the school building for another year without knowing that the Ultimate Despair members were already in their midst. However Kyoko Kirigiri began to piece together that there was not only one, but two members sealed in the school as noted in her journal, but wasn't able to share this information with anyone before the killing game began. To ensure Junko could monitor the game from the outside and not raise any suspicion, Mukuro disguised herself as her sister and pretended to also be a victim forced into the killing game until she was able to exit via faking a rule break after the first murder. However, Mukuro was ultimately betrayed by her sister, who instead of removing her from the game after she stomped on Monokuma, impaled her on the spot with Spears of Gungnir. Mukuro was not expecting the betrayal, so she failed to save herself and succumb to her wounds moments after uttering out her final words: "H-Huh? This wasn't...supposed to... Why...me...?" As the killing game progressed, Junko used Mukuro's corpse as a trap for the remaining students. Junko planted her corpse in the Greenhouse on the fifth floor of the school rigged with a bomb and evidence to imply that the hidden sixteenth student "Mukuro Ikusaba" had died as a result of murder. Mukuro's corpse was set aflame by the Monokuma Bomb leaving only her lower body and hand undamaged as well as the impalement marks. The truth was eventually discovered and revealed by the remaining students that corpse was the true Mukuro Ikusaba they had met and that her sister was the one behind it all.