Selfless

How did Enrnanfo become the strongest martial master again?

It is by putting only anger instead of an empty mind as he practiced Enzen Breathing. No other emotion should be placed as it will only distract him. 

When he was left behind by the woman he loved the most, he realized he was betrayed, no, worse. At that moment, there was only anger in his heart. Instead of ruining the technique, his anger was so pure that it actually became a drive.

There are three forms of Enzen Breathing.

The First Form would be the most passive, healing him and rejuvenating his body while he cannot move. The Second Form is flexible - most used for a battle of attrition, bringing out his battle capabilities while still sufficiently recovering his energy. The Third Form is an all-out form, using all his energy until it turned to nothing.