己: Self and confidant. Knowing oneself and understanding others leads to invincibility in all battles. —"The Art of War" by Sun Tzu.
桦: The tree species, birch. "Birch" symbolizes the toughness akin to a tree, unyielding to wind and rain, metaphorically representing a robust physique conducive to good health.
Meaning: Self refers to individuality, while birch symbolizes resilience and purity.