The goal of this clinical trial is to verify that Non-Antithrombotic Therapy (NAPT) followed by Oral Anticoagulants (OAC) monotherapy for 45 days after Left Atrial Appendage Closure (LAAC) is non-inferior to Single Antiplatelet Therapy (SAPT) with aspirin during the period from randomization to the end of observational period (4 years at the maximum) in non-valvular atrial fibrillation subjects with high bleeding risk. The primary endpoint is a composite endpoint consisting of all-cause mortality, myocardial infarction, stroke, systemic embolism, major bleeding, or clinically relevant non-fatal bleeding from randomization to the end of study observation (up to a maximum follow-up of 4 years). * Participants will be enrolled in this study until the day following the implementation of LAAC and will be randomized to the SAPT arm and NAPT arm in a 1:1 ratio. * Participants will be observed for 4 years from the time the first subject is enrolled in this study. * Participants will visit the hospital at 45 days, 1 year, and 2 years after enrollment, and will also be followed up by telephone, basically at the end of the observation period (up to a maximum follow-up of 4 years). \<Study treatment duration\> In both arms, OAC monotherapy will be initiated in the first 24 hours of enrollment and continued for 45 days (allowed window period: plus 2 weeks).. * SAPT arm will continue to receive 45 days of OAC monotherapy followed by low-dose aspirin (75～100 mg/day) as an antithrombotic agent required through the end of the study observation period. * NAPT arm do not receive antithrombotic medication after 45 days of OAC monotherapy through the end of the study observation period.