A 12-year-old severe hemophilia boy had developed inhibitor since he was two. At 10 years of age, he received high dose factor VIII after plasma exchange in addition to bypassing agents for treatment of CNS bleeding, causing peak inhibitor titer of 3,360 BU. ITI was initiated when his inhibitor was decreased to 140 BU, and the prophylactic emicizumab had been added since the second year of ITI. After 3.5 years of ITI and emicizumab, his inhibitor titer was down to 0.56 BU (factor VIII recovery was 60% and half-life 5.5 hours). His QoL was remarkedly improved and without bleeding.