Finally got the platinum! XD
The most tedious trophy in this game is 雑貨マスター, which asks you to collect all wall, table and floor items.
Once you’ve tried everything (give a lot of presents to Vocaloids, max their affections, make them angry then make up with them, use the gadgets, advance Vita clock etc etc), the last item you would probably unlock is びっくり時計, a wall item.
びっくり時計 can be unlocked simply by keep fulfilling Vocaloids’ requests (they will make requests if you pet them in the head often enough). Just like giving presents, it would be a while before you get the last item (there’s quite a gap from the second last item).
Got the item after petting Ren:
Buy it in store:
I was lucky that I have been petting them here and then. It’s because I was working toward クラスタ trophies (raise Vocaloids’ affection to level 5) and noticed that I still kept getting items, so I kept petting them. For those who have been ignoring this, the grind might take longer ^^;
I checked, and apparently I was the 6th to earn platinum in PSN Trophy Leaders. Well, this was the highest position I ever reached in a trophy race, I guess ^^;