He works with the Satsujinzoku to kidnap Eigetsu Tou and Kōrin (whom they had mistaken for Shūrei); believing that the group is under his grandfather's control, he attempts to shift their allegiance of their leader, Meishō, and gain their support for himself.
He works with the Satsujinzoku (whom they had mistaken for Shūrei). This was to kidnap Eigetsu Tou and Kōrin. The group is under his grandfather's control. This is what he is believing. He attempts to shift their allegiance of their leader and gain their support for himself. Meishō is their leader.