sekai ka kanojo ka erabenai

one day, kouki nakagawa was determined to declare his love to ayumi fujisaki, his childhood friend. suddenly, a mysterious girl appears before them and mentions that she is kouki’s girlfriend, leaving both perplexed. after trying to talk to ayumi again, kouki confesses his love to her; but jindou, the mysterious girl, appears to warn kouki that if he does not accept to be her boyfriend and does not forget ayumi… the world will be destroyed!