As you explore the many maps of One Piece Odyssey it's inevitable that you'll come across at least one locked treasure chest. They're all over the place, and the only hint you receive towards opening them is Nami insisting that you come back once you have a Treasure Chest Key. Alas, you won't get said key for quite a while... though once you do, there are many, many items for you to collect.
This guide will lead you to all of the locked treasure chests in One Piece Odyssey. First, though, you need to claim that danged Treasure Chest Key.
Grand Line Quiz Side Story
When you first arrive in Alabasta's Sandy Oasis you can undertake a Side Story known as Grand Line Quiz Kid. This is the first of four similar Side Stories that will follow you from one section of Memoria to the next, ending when you reach Dressrosa. Each one consists of answering trivia questions regarding One Piece as a franchise, often above and beyond the scope of this game.
The Side Stories you need to complete are the following:
Note that you must complete these Side Stories in this order, or the next one in line won't appear. Complete all four segments of the Grand Line Quiz and you'll receive the Treasure Chest Key. At that point you can go around opening all the locked treasure chests that you please.
Waford
- Waford South, Forbidden Valley. Climb down into the valley in the southwest of Waford. After going down the first length of vines, look to the north to see a chest. This chest contains HP Conversion Jewelry.
- Waford South, Forbidden Valley. Climb all the way down into the valley, then enter the narrow cave paths in the north with Chopper. You'll find the chest within the second cave. This chest contains HP Auto Regen Jewelry.
- Waford South, Path to Eastern Ruins. Cross the bridge from Adio's hut to the Ice Block Ruins. There's a small chamber only Chopper can reach near the stairs up to the ruins. Inside is a steel door for Zoro to open, and beyond the door is the chest. The chest contains the Waford Ring.
- Waford South, Hermit's Cave. Go through the small tunnel with Chopper on the path to the Dust Ruins to find the chest. If you've been fusing accessories with Madame Julie you have a Yoisa Travel path straight to the cave. This chest contains TP Auto Regen Jewelry.
- Waford South, Circular Inland Sea. Grapple over to the large clearing on the east side of this area, then grapple along the columns to the north of the clearing. The chest is on the other side of the columns. This chest contains Shock Element Jewelry.
- Waford South, Waford Central. Near the campsite at the base of Sky Tower is a cave for Chopper to traverse. On the far end is a door that Zoro can slice through if you max out his Door Slice Skill. The chest is beyond the door. This chest contains a Wild One's Necklace. Robin can also find Information on the Strange Place sitting near the chest.
- Sky Tower, Strange Cube Floor Level 2. Go up to the first platform when you first arrive in this area of the Sky Tower and look on your right. This chest contains the Waford Necklace.
- Sky Tower, Strange Cube Floor Level 3. As you head south along here you can create bridges between floor buttons. Generate them towards the southwest of the area to find a platform by itself, then grapple over to find the chest. This chest contains the Odyssey Necklace.
Alabasta
In order to reach two of these locked chests you'll need to build bridges with Franky. Franky requires Carbon Bolts and Junk in both cases. Both are found in Dressrosa, though you'll need to consult the guides for Dressrosa to learn where to find the Carbon Bolts, as they're quite limited in number.
- Nanohana, Eastern Highway. Walk as far east as you can along the Eastern Highway. In the far northeast of Nanohana and at the top of some stairs you'll find a small back alley that only Chopper can reach. The chest is in the alley. The chest contains TP Cost Reduction Jewelry.
- Desert Near Nanohana, Desolate Valley. West of the campsite in the north of this area is a cave only Chopper can enter. Past a huge skeleton you'll find a point where Franky can build a bridge for three Carbon Bolts and fifteen pieces of Junk. On the other side you'll find two normal chests, containing Sandora Dragon Steak Tips and Mr. 5's Booger, and the red chest. This chest contains the Waford Crown.
- Great Sandy Desert, Bone Bridge Canyon. Travel west through Bone Bridge Canyon - by ground, not by grappling - and you'll find a point for Franky to build a bridge in the northwest. This costs two Carbon bolts and ten pieces of Junk. On the other side you'll find a normal chest tucked away in the back, containing three Volcano Dragon Tails, and the locked chest. This chest contains Evasion +20 Jewelry.
- Great Sandy Desert, Sandy Ruins. Proceed through the area towards the north of Great Sandy Desert until you reach the huge yard of bones where you encountered a Leviathan early in the game. The chest sits in the middle of the Leviathan's treasure pile. This chest contains TP Regen Jewelry.
Water Seven
- Water Seven City Area, Cafe Park. Enter Cafe Park from the southern bridge, then look to your left. If you head west along the water you'll find three pillars tucked under the side of a building. The chest is hidden behind these pillars. This chest contains HP Auto Regen Jewelry.
- Water Seven City Area, Fountain Square. In the northeast of Fountain Square you'll find Red Bird Apparel, a clothing store. The chest is on the right side of the front desk. This chest contains TP Auto Regen Jewelry.
- Dock One, Material Depot. Head west from the entry bridge and use the crane at the other end of the Material Depot to get at the rear of the storage sheds. Explore to the east until you find a spot that Chopper can fit through inside one shed. On the other side you'll find the chest. The chest contains Death's Edge Power Jewelry.
- Sewer, Old Sewer. Entering from the southeast, proceed through the Old Sewer until you pass the larger room with the water at the bottom. The southwest room of the Old Sewer has a break in the wall on its lower level, and the chest is inside. This chest contains the Odyssey Crown.
- Sewer, Old Sewer. Head two chambers north of the room where you found the previous locked chest. In the northeast corner of the room, tucked behind a raised platform on the lower level, is a second chest. This chest contains TP Regen Jewelry.
Marineford
- Town Outskirts. Run north down the street from the Memoria Cube. You'll see two men, a dog, and a tree on your right. The chest is behind the tree. This chest contains TP Auto Regen Jewelry.
Dressrosa
- Dressrosa City Area, Dressrosa City East. Look northwest of the Yoisa Sign and you'll find a passage only Chopper can bypass. Check by the stairs of the house on the east side of the clearing beyond the passage. This chest contains Freeze Element Jewelry.
- Dressrosa City Area, Blacksmith Road, north of the Coliseum. In Rose Guerrero, a weapons shop, on the east side of the street. This chest contains Fire Element Jewelry.
- Dressrosa City Area, Coliseum Path. Head to the book store to the northwest of the Coliseum entrance, then check the pation paths to the east. The chest is up some stairs leading to the front door of a pink house. This chest contains Wild One's Crown.
- New Royal Plateau - 1st Area. Head north towards the Sewer. Beneath the bridge-and-stairs combo that Franky built to reach the entrance to the Sewer is a ruined street with several collapsed homes. (You may remember a crying woman, if this helps with navigation.) Grapple down to this ruined street and keep an eye on your left as you walk west along it. This chest contains Evasion +20 Jewelry.