The Snow Fable: Mystery of the Flame (EP)

Actual unlock requirement is to use the Fire Spirit 100 times, not 25 as suggested in the achievement description.

The Fire Spirit is unlocked in Chapter 1-5.

If you have any remaining (can be tracked using Statistics from Main Menu) the fastest method I found was:

Load Chapter 1-5
Follow the prompts to power up the Fire Spirit
Select Fire Sprit with then press to Use
Press , Replay, OK.
Rinse and repeat until Achievement Unlocks.