In June 1406, his father Akinori died; on November 20, 1406, only a little while after Mitsunori succeeded the family estate, Nagaharu OGASAWARA, the provincial governor of Mikawa Province (the Hazu-Ogasawara clan), and his son Nagayori were captured in Mitsunori's residence in Kyoto, and were imprisoned in Ishikawa-jo Castle in Tango Province.
応永13年（1406年）6月、父・詮範が死去し、満範が家督を継いで間もない10月1日、京都にある満範の屋敷で三河国守護代小笠原長春(幡豆小笠原氏)・長頼父子が捕らえられ、丹後国石河城に監禁される事件が起こる。