I wanna know the details about calling a new guard and sensai tile acquiring.
1. When I defeat a guard called Mr.A, I choose banzai.
Now Mr.A is discarded, and draw a new guard to replace Mr.A's place?
2. Can I use +1/-1 dojo card to acquire sensai tile? Or just one dojo card to acquire one sensai tile.
1. No, subsequent guards do not take the place of preceding guards. If Mr. A is the sentry for the house (the 1st guard) then Mr. A is only discarded if the house is cleared of all treasure. Otherwise, Mr. A remains and subsequent guards are discarded as defeated (or even if they aren't defeated). In short, the only time a sentry guard is discarded is when a house is cleared (and then they are only replaced in the following round when the house is refilled with treasure).
2. No skills or cards can be used to modify the dojo card used for acquiring a sensei card. You must discard one dojo card exactly matching the sensei tile.
See #'s 1 and 10 here.