I have completed all other stories and nothing happens?
Seems you already completed the Nani Task. The only other requirement for that task to happen is to buy a weapon at Story store which you seem to have already done.
How are the other characters in the journal looking? When completing tasks listed at the lowest day, you'll never get stuck. I think you've neglected a few characters making certain tasks not trigger.
If that's not the case, feel free to send me your save file and I'll have look.