Seems as though they have been working together all along to perfect ichigo's powers and catch him off guard
I read through it again. I'm guessing that
Ginjou's blade actually works as "Book of the End" does, and cut Tsukishima with it in order to control Tsukishima to make him look as an enemy and himself as the goodguy. And as you said, helped in the development of his powers in order to steal his perfected fullbring. It makes sense, Ginjou being
The Only One in close contact with inoue, chad, and Ichigo's friends and family. I don't know how I came to the conclusion, but I think the Rukia is giving away her powers for ichigo to take, which is what his dad is doing xd