(credit to KikujiroChan, the person who discovered the skip)
First trip to B1
upright until he drops, then go right
go down through stairs, PP,P (or PPK)
pick up the Nikita
Second trip to B1
left cartwheel, then 2.5 step loops downleft, down.
If you see the third column on the right, adjust to the left/right.
You can judge if you are too far left or right by Raiden's position in the camera(?)
PP,P (or PPK) at the invisible stairs, climb up invisible stairs
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