Lost Sphear isn’t too hard of a platinum and more in line with I Am Setsuna. It will probably take around 40-50 hours to get everything. The platinum is fairly straightforward and you don’t have to worry about any missable trophies. You have your usual assortment of story trophies, then the rest will require you to do various gameplay stuff. One quality of life thing, if you wish to rush through things, is the ability to speed up story scenes by holding down the Options button.
Step 1 - Play the Story
Your first step will be to play through the main story. Note that there are no difficulty-related trophies, so you can play the game on Easy if you wish. As mentioned above, you can “skip” scenes by holding the Options button down (it will say this in the bottom right corner when you can do it). You might get a few other trophies along the way, but nothing is missable for the platinum, so you can wait until after you defeat the final boss to do those.
Step 2 - Character Sidequest
Once you’ve reached the final story dungeon, you will unlock the ability to do character sidequests. Each character in the game have their own sidequest, as well as a trophy associated for every quest. All of the sidequests will have a boss to fight at the end, which aren’t too difficult, so it shouldn’t take more than 20-30 minutes to complete each one.
Step 3 - Gameplay Related Trophies
With the main story and sidequests out of the way, you can concentrate on the gameplay-related trophies. A good number of them are pretty simple and will likely unlock through the course of naturally playing the game, but others will require some grinding. The biggest culprit will likely be Vulcosuit Master, which will have you using all of the Paradigm Drives in the game.
Step 4 - Cleaning Up
If you still have trophies left over after performing the above three steps, then you can go around and do those in this step. These will likely involve the specific foods you have to eat, consuming 100 meals, and the money-related trophies. This step shouldn’t take too long and once it’s over, you will have a shiny new platinum.