Dusk Diver 2

This is a rather simple trophy wherein all you have to do is to upgrade any skill on any character for the first time. However, you won't be able to do this until the beginning of Chapter 8, when you're able to upgrade your weapons to Rank 8. Once a character's weapon is at Rank 8, you'll be able to upgrade all 3 of that character's original SP skills.

All skills in this game unlock depending on your weapon rank, not your level. (See Top Craftsman  for more about weapon ranks.) Each character has Combo Skills and SP Skills that you can spend Wafers to purchase depending on your weapon rank. Combo Skills typically unlock every few levels starting from the beginning, but new SP Skills can't be purchased until Rank 8 and on.

To upgrade (or purchase a new) skill, press Options to open the Menu > go to Battle Prep > click Learn Skills > scroll down past the Combo Skills to the yellow blocks, where you can upgrade the already-owned SP Skills. For the first 3, they'll cost either 4000 or 6000 Wafers.