When Roan was guiding everyone to open the little hole to reach the Fragment, the hole Leandro saw wasn't the only one being made. Another one, behind Rean's hand, was also being made. It wasn't possible to look through the Purple Crystal due to the dense Chaos Laws and Energy inside it, so there was no way someone else could see that second hole.
Rean already had the item Kafan gave him, which was very small, even smaller than the Foreign Universe Foundation Fragment. One hole was made so Leandro would be able to see the Fragmetn at the center of the Purple Crystal. The other hole was made coming from the opposite side. As the little bead Kafan gave Rean was smaller than the Fragment, the Fragment itself served as a cover for the second hole.
The main point of the plan was to attach the item Kafan gave Rean to the Foreign Fragment without activating its ability to send the Fragment out of the Universe. At the same time, it had to be there without anyone noticing.
