To begin Shinya Oda’s Tower Arcana, you must first complete the ‘Ose’ Mementos quest by defeating the boss.
Once you encounter Ose, exit the Memento and head towards the Shibuya arcade to finish the quest.
Next, go to the Akihabara arcade center and talk to the boy wearing a hat.
This will initiate the Tower Arcana quest line.
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