A Hat in Time

This should be your final achievement if you went to the time rift already and got all the time pieces. You start with three stickers already in your inventory so you need to find 30 more that are specifically in Nyakuza Metro's free roam area.
https://steamcommunity.com/sharedfiles/filedetails/?id=17386...
Linked is a guide that does a much better job explaining that I ever could. If you want to see how many you have just pause, go to the stickers on your weapon, and count all the stickers you have minus the three you start with, Cat Crime, heart, and the star.