Sasaki Isaburou is the commander of Mimawarigumi. His character is based on the leader of the real Mimawarigumi, Sasaki Tadasaburo.
Sasaki Isaburou was born into the elite samurai family Sasaki, as the main heir. He is also the half brother to Sasaki Tetsunosuke.
His personality is completely different when writing e-mails by cellphone. He insists people to call him Sabu-chan and states that he doesn't have many friends. He cannot express his feelings well by speaking, so he usually texts with his cellphone. He also has a need to express Mimawarigumi's eliteness.
Isaburou trusts Nobume's abilities as an assassin and as his most loyal member of the Mimawarigumi. He also seems to know very well about Nobume's love for donuts and uses it as a reward for her good work.