Backstory about the tissues: Matsui Rena has attended MS for a number of times, but she attended them as a member of AKB. Not SKE.
Everytime you attend MS, you get a box of tissues as a souvenir. But Rena feels that she, as a member of SKE, should attend MS with the rest of SKE. And so she left the tissues there and never brought them back.

This time. She attended MS as a member of SKE. And so she can finally bring all the tissues home.