I think you should get some sleep too.
It kind of made sense to me (at 2 am).
Killing Shizuha would not be easy, so Senzui had to come up with a good plan to catch her off guard. He would lure Saiga away from her (Our friends in remote location X are being attacked and need help NOW) and tell Saiga that he would stay with Shizuha while telling Shizuha that he'd go with Saiga or find some other excuse to leave (Our friends in location Y are being attacked as well).
He'd then order some capable but replacable clan members to go for Shizuha's group who were probably hiding somewhere they thought to be relatively safe, because Shizuha had a little baby with her. One part of the group would go for Shizuha and her companions while ramdom kuremisago gunman would sneak up from the other side. Senzui didn't actually expect this guy to succeed, because Shizuha was way to skilled for him, but it would give him an excuse to appear as Saiga and "save" her. The false Saiga would suddenly appear in this chaos when most of Shizuha's friends were already dead/dying and kill replacable gunman z, to make his guise more believable. He could later tell the others that this guy was killed by Shizuha, so noone whould miss him or ask questions.
Shizuha falls for his ploy -> KILL