Elena Aoki, Clair Aoki's older sister, transformed into a monster and murdered their parents, disguising the killings as a poison gas incident. She despised their corrupt politician father and mother, who had an affair with a younger coworker, viewing them as hypocrites. Sparing Clair, Elena claimed the act liberated her sister from their parents' toxic influence, referencing Clair's past wish for their deaths, and gave Clair a coin for potential use. At Yamada Cram School, Elena befriended Shuichi Kagaya, Honoka, Kaito, Naoto, and Aiko, later dating Shuichi and welcoming transfer student Sayaka Koyanagi. After Honoka used an alien coin to assume Aiko's identity post-Aiko's suicide, and Kaito's wish turned Honoka into a memory-erasing monster, Elena used coins to transform herself and Shuichi into monsters for survival. She erased Shuichi's memories of their relationship to shield him from Honoka and conceal her vulnerabilities. Emotionally volatile with violent tendencies, Elena harbored a yandere obsession with Shuichi. She attempted to merge with him by entering his monster form, flying into a murderous rage upon sensing another girl inside—initially unaware it was Clair. Her overwhelming power dwarfed Shuichi's, and her history of murders left a lingering scent of death that terrified both Shuichi and Clair. In human form, Elena appears as a fair-skinned young woman with short dark hair, red eyes, and a slim build, often wearing a brown hat. Her monstrous form manifests as a towering ghost-like entity with long hair and a skeletal mouth, capable of disassembling into ash for teleportation. She possesses immense strength, demonstrated by beheading Shuichi's monster form, and can manipulate memories. Elena co-led a coin-collecting group with Naoto, targeting 100 coins for a wish against Kaito's monster. She commanded loyalty from Subaru, a powerful collector she occasionally showed concern for while viewing him as a child. During a confrontation with Shuichi and Clair, Elena tearfully apologized for transforming Shuichi and accepted his right to kill her—until hearing Clair's voice from within him triggered an attack. Recognizing Clair, she provided another coin and departed.