We each kept a copy of the contract. The System made a copy of it so that each of us could keep it, and opened a rift to teleport it somewhere. That was when I found out how bad it was too make a new rift in a reality.
Space twisted and tied, then tore. It was a sensation that would have made me throw up without my new constitution. As it was, it made me quite green in the gills. But that wasn't the worst of it. After the rift shut, a scar in reality remained. I could tell that it would be easier to rip spacial rifts there in the future, and space all around it was stretched somehow.
I looked at my kidnapper. The System no longer controlled his body, but he was out cold. At least it didn't seem to have done any mental harm to him from what I could sense. I would have to tell it when he woke up that space rifts were best kept to a minimum.
In the meantime, I needed to store my copy of the contract also. I was unwilling to create a new spatial rift; not that I had my own personal reality to put it in. The idea of space being stretched too far and ripping apart was too frightening to risk.
There was a way to do this without stressing an already stressed reality further, though. I just had to make my own reality and set up my own Creation System with a personal inventory bag or wallet. A stable rift would be harder to create, but I already had noticed that the rift the castle doors in this pocket reality opened put a lot less strain on the surrounding space.
So I reached out again. At the end of the vast orchard I had created, I spoke into existence a heavy metal door, with bars and bolts galore. While the locks wouldn't actually keep anyone out, they would at least say, "Don't go here."
Then I spoke a box reality into existence; forty stories high, wide, and deep. This was a reality where items did not undergo any changes, but sorted into neat sections by type.
I made a magical satchel that was bound to me with a knot of space, and that was so heavy that no mortal could hope to even open it, let alone lift it. It could display a representation of the contents of the box space once connected to it.
Now for the tricky part. Opening a spacial rift wasn't hard in of itself. The hard part was connecting to a specific reality, not to some weird version of Hell.
Then there was the interesting concept of making it stable, then movable. Stability was easily achieved by sealing the opening of the satchel to edge of the item box reality. Making it movable however, required some investigation. The rift was, in effect, covering they mouth of the satchel. The whole satchel could be said to contain the new pocket reality, and the space of even a normal satchel changes its connections constantly due to its container. I simply copied the natural spacial effect I observed.
While I was dropping the contract into my new inventory bag, I heard a groan. The poor unfortunate soul who'd kidnapped me, gotten punched in the face, waited for days to be let back into his pocket reality, and then was possessed by his System was waking up.