Japan's National Tax Agency has reported a significant increase in tax reassessments related to personal cryptocurrency transactions. From July 2024 to June 2025, the agency conducted 613 on-site investigations, resulting in additional tax collections totaling 4.6 billion yen, a 31.4% increase compared to the previous year. The average reassessment amount per case was notably higher than the average income tax level. The agency identified unreported amounts totaling 15.6 billion yen, with key risk areas including unmerged declarations across multiple exchanges, improper handling of DeFi and airdrops, and incorrect timing for mining and staking income. Non-declaration could lead to an additional tax of up to 20%, while deliberate concealment could incur penalties as high as 40%.