- Estimated achievement difficulty: 4/10 [Achievement Difficulty Rating]
- Offline: 88 
- Approximate amount of time to 1000: 100+ Hours [Estimated Time to 100%]
- Minimum number of playthroughs needed: 2
- Missable achievements: Lone Traveler (50G), Fleetfoot (50G), Treasure Hunter (25G), Strategist (25G), Eagle-Eyed (25G), Collector (25G)
- Does difficulty affect achievements: N/A
- Unobtainable/glitched achievements: No
Eight travelers. Eight adventures. Eight roles to play. Embark on an epic journey across the vast and wondrous world of Orsterra and discover the captivating stories of each of the eight travelers.
Step 1: 100% Run
Essentially, this is what I would suggest you do, with missables marked in red.
- Pick a starting character. Cyrus is a good choice since he has the Analyze ability to quickly begin working on enemy weaknesses. I chose Ophelia though and then went clockwise around the lake to recruit all the characters (Cyrus being second), as this is also the order the walkthrough I linked above did it.
- Recruit two more characters and complete Chapter 1 of each, while also exploring their starting areas. Make sure you fully analyze the Meep (Flatlands) and Cactus Roller (Sunlands) enemies at this time, BEFORE recruting a fourth character.
- After recruiting Alfyn, get the hidden item from Meryl before doing her side-quest and get the hidden item from Zeph before finishing all Chapter 1 quests.
- Bring Cyrus along when recruiting H'aanit, and get the hidden item from Lord Ciaran's Herald before finishing the Chapter.
- Finish recruiting all characters and explore all starting areas.
- Complete five Chapter 2 stories. Before completing a 6th Chapter 2 story, fully analyze Sea Birdian 4 and Buccaneer 1 weaknesses in the Coastlands.
- During Cyrus' Chapter 3 story, get the treasure chest when you are in the pit.
- During Olberic's Chapter 3 story, get the hidden item from Bale in Wellspring.
- During Primrose's Chapter 3 story, steal the "Obsidian Garb" item from the chapter boss.
- In Duskbarrow, get the hidden item from Crest-bearing Swindler before fighting him.
- During Cyrus' Chapter 4 story, scrutinize "From the Far Reaches of Hell" LAST to get the "Original Tome" item.
- When doing Ariana's quest in Stillsnow, get the hidden item from the Traveler NPC in Trail to the Whitewood.
I personally used the team of Ophelia, Cyrus, Therion, and Olberic for most content. You can mix and match as you'd like, but the four I used and the backup four all have similar Path abilities (Ophelia Guide = Primrose Allure, etc), so you'd want a straight swap rather than having two people with the same ability in the party or you may not be able to do everything needed. However, Therion over Tressa was essential since he's the only one who could open locked chests, and stealing items versus purchasing them was much better in my opinion (though you'll be swimming in money at the end of the game, so anything with a low steal chance, just swap her in and purchase it later).
When thinking about secondary jobs, you can get things that complement the main job or diversify to cover more options. For instance, since I didn't have Tressa on my main team, having someone with the Merchant job was helpful for wind magic and her ability to hire help in combat. Once you get the hidden jobs though, those tend to be better than anything else available.
Step 2: Post-Game Cleanup
After completing all the inidivudal stories, you'll need to finish up every side-quest which includes tackling the end-game dungeon in the Ruins of Hornburg as well as the superboss Galdera. One thing the Neoseeker guide I linked above didn't mention which makes defeating this superboss SO much easier I have mentioned in the accompanying achievement description below. I tried and failed many times on that boss even way overleveled before I added that piece to the strategy.
After defeating this boss, you should get your last item needed for the collection achievement, though there are a few rare ones you may not have come across naturally which I've mentioned below. The accessory you get from the superboss is actually very useful - it will turn off random encounters, which will make collecting any missing items or treasure chests go much more smoothly. At the end of this step, you should only have two regular achievements and the "platinum trophy" achievement left to earn.
Step 3: Solo Speed Run
It is suggested you use Tressa for this, but it's certainly possible with every character. These should be your last two achievements, so see the guide below for links to Youtube videos for every character.