His son Tokugawa Ieyasu was adopted by Naotora and , under Ii Naomasa , became a dreaded general , who is considered one of his four guardians . His son Tokugawa Ieyasu was adopted by Naotora , and became a feared general under Ii Naomasa , who is considered one of his Four Guardians . His son Ii Naomasa was adopted by Naotora and became under Tokugawa Ieyasu a dreaded general , who is considered one of his four watchmen .