On April 15, 2023, an assassination attempt occurred on Prime Minister Kishida of Japan during his support speech for a by-election in the National Assembly. The verification results indicate that the swift and appropriate response of close protection personnel succeeded in ensuring the Prime Minister's safety, but fundamental threat mitigation, such as preemptively thwarting the terrorist's attack attempt, was unsuccessful. Analyzing the assassination incident through the Security Organization Variation Model, it is anticipated that Japan's security organization will continue to evolve due to various pressure factors, including changes in the political sector, demands from the public, and potential threats from anti-government figures. The Japan National Police Agency is formulating additional measures to address issues arising from these pressures, but the related solutions are primarily focused on countering anti-government figures. Moreover, these measures are inadequate without accurate awareness of lone-actor terrorists, a new form of factor terrorism. To prevent future incidents of mimicry terrorism by lone actors who are not affiliated with specific terrorist organizations and have no history of mental illness or criminal records, practical measures such as multi-layered screening at event venues and risk analysis through the aggregation of relevant intelligence by public security authorities during peacetime are necessary.