Yakuza Kiwami is an action adventure game and a remake of Yakuza from the developer and publisher Sega. In the game, you have to find locker keys for a total of fifty coin lockers. In these lockers, you find many different items such as potions, weapons and equipment. You can sell these items for many yen at the Ebisu Pawn Shop. These items are extremely useful at the beginning of the game.
All Coin Lockers can be found in the center of Kamurocho as in the previous game. Just to the left of the Millenium Tower, you can unlock fifty lockers with correct keys that are scattered across the map. The keys are named from A1 to J5 and the following video shows you their locations.
Before you look for the keys, you should pay a visit to Bob Utsunomiya. For this NPC, who is appeared like a clown, you can exchange CP (Completion Points). You get these by completing activities in the game (for example, eating in restaurants, playing mini games, defeating opponents, etc.). Bob Utsunomiya is located at the entrance to Tenkaichi Street in the south west of the map near the taxi stand (check out the below video to find his location)
If you have collected five Completion Points, you can exchange them for the Key Keeper. This will cost you 3 CPs, but you must first score two points for Gotta Go Fast Lv. 1 so that the Key Keeper can be enabled. The Key Keeper can be equipped later. If you are near a Locker key, the Key Keeper starts to beep, which makes it easier for you to search further.
Note the following peculiarities for some keys
I4: You will find this key in the West park, where you only gain access later in the game.
B5: You can enter the underground casino area later in the game. Here you will find the key half way.
I3: You will get the Sub story 23.
C1: You will get the Sub story 42.
J5: You will get the Sub story 43.