• 自己じこ — self
• 自己紹介じこしょうかい — self-introduction
• 利己りこ — selfishness
• 利己主義りこしゅぎ — egoism
• 克己こっき — self-control
• 知己ちき — close acquaintance / confidant

己 may trace to a coiled or curved form and later came to signify the personal self. It’s also the sixth of the Ten Heavenly Stems (十干), appearing in calendrical terms.

自己じこを 見みつめることは 成長せいちょうの 第一歩だいいっぽです。
Reflecting on yourself is the first step toward growth.

己おのれを 知しることは 難むずかしい。
Knowing oneself is difficult.