Focus Spirit is a skill that can be activated by a warrior once his Magic Gauge (green bar on the top left corner of the screen) is full. While active, the warrior can't be staggered or stopped by any attack (though he/she will still lose hearts if hit) and will gain significant boosts to attack power, attack speed, and defense. Furthermore, this skill gives the player bonuses for defeating enemies while this skill is active.
The Focus Spirit gauge slowly drains once activated but it can be replenished by 25% for every 50 enemies killed. And for every 50 enemies defeated, a new bonus effect is activated on top of your current active bonus effect. That's why it is recommended to use this while you're in the middle of an enemy horde so you can stretch the Force Spirit's duration by killing enemies as fast as you can. This doesn't mean that the effect can go on forever. The Focus Spirit recovery seems to stop after you reach 200 kills.
Before the gauge is completely depleted, players can unleash a powerful Focus Spirit Blast by pressing the SP Attack button. This will drain the remaining Magic from your gauge and stop the effects of Focus Spirit prematurely. However, ending the Focus Spirit effect using this method will also reveal the enemy's Weak Point Gauge, including bosses. If you're not able to use the remaining magic to unleash this attack, your warrior will automatically use a different Blast, which is usually a crowd-clearing skill.
You can replenish your magic by picking up Green Bottles dropped by enemies, found by clearing out the small grass fields in the game, or simply breaking green jars.
Rewards
25 KOs | More Rupees |
50 KOs | More EXP |
75 KOs | More Hearts |
100 KOs | More Rare Materials |
130 KOs | More High-Rank Weapons |
Young Link may also be the best character for this as he can replenish his Focus Spirit by trading his Specials for longer duration. I have seen countless YouTube videos on his skills with Fierce Deity at his disposal.
I believe that the players upgrade Focus Spirit and Din's Fire completely in the Bazaar.
https://www.youtube.com/watch?v=ChesrN7aF1o