This article examines the success rate of prosecutions in Japan and explores the factors that can affect it. The success rate is high, with around 90% of criminal cases resulting in convictions or guilty pleas from defendants. However, there are challenges faced by prosecutors in obtaining sufficient evidence against suspects due to privacy laws and fear amongst potential witnesses about retaliation from suspects. To improve the success rate, measures should be taken to address these issues such as passing legislation to increase access to information for investigations or providing more protection for witnesses who come forward to testify.