Hello!
They keys are already all implemented, just a bit difficult to obtain! Here is a list of all the keys and their locations I've copied from our discord:
Squid key (Bathhouse) - After you checked on Mira after the first trial (it should be at the time the banquet is being prepared), don't skip the time by going to sleep, there is a merman in the kitchen that will ask for your help with taking the trash out. You need to collect all the trash in the kingdom and bring it past the garden, like he says.
Shell key (Storage Room) - In the meeting room is a vending machine, you can use it to get different kinds of items and with a little luck you'll get the shell key from it!
Octagon key (Break Room - When telling the guards that you want to partake in the trials and they ask you to get the cleaning supplies, check the cleaning supplies in your inventory before handing them over! You'll find the octagon key in them!
Triangle key (Garderobe) - There is a mermaid in the break room which asks you to get a bucket from the meeting room that she forgot there. If you finish that quest and report back to her, she'll reward you with the triangle key.
Fish key (Freezer) - I believe it's on your first evening there, when it's dark, go to the path to Neptune's Throne room and talk to the, from your character's perspective, left guard. You'll be prompt with the decision of either "distracting them" or "Leave". You'll want to distract them. After that is done, sneak into Neptune's room and find the bunch of flowers behind him to his left. That's where you find the key. Be sure not to run though, cause then you'll get caught and it's gameover!
I hope this helped!~