After completing the Highway Story mission in which you infiltrate a Grub-infested underground bunker, you’ll be given the opportunity to help Ayame with one of her side projects. Finding information about the popular idol OK!-chan can be a bit tricky as the game doesn’t give you any real guidance. How to complete Find OK!-chan side quest in Anno: Mutationem.
After the highway mission, you will appear in Noctis City. Go to the bright billboard with OK!-chan to start the side quest. You’ll first need to find and speak to a handful of NPCs that are helpfully marked on your map. There’s nothing special you need to do other than talk to them before you’re eventually directed to a building where OK!-chan is said to live. Upon entering, their synth pop can be faintly heard from an upstairs room, but the room is sealed tight.
Go downstairs to the ground floor and peek through the peephole. You should see a pattern on the table at the bottom right – this is the passcode for the door above. Although it’s a strange place for a puzzle solution, get these three symbols in the door. Go inside, find out the identity of OK!-chan, and then return to the quest giver to get your reward of 400 Grombits, 1 Grom Upgrade Point, and some cash for your wallet.
https://www.gamepur.com/guides/how-to-complete-the-find-ok-chan-side-quest-in-anno-mutationem How to complete Find OK!-chan side quest in Anno: Mutationem