自 was originally a picture of a nose seen head-on. East Asian people had the habit of pointing at their own nose to say "me," and so the character that drew a nose shifted to mean "self, oneself." The original sense "nose" split off into 鼻 (bí), which added 畀 (bì) below to preserve it.

Mandarin: zì, 4th tone. 自己 (zìjǐ, oneself), 自由 (zìyóu, freedom), 自行车 (zìxíngchē, bicycle — "the vehicle that goes by itself"), 自来水 (zìláishuǐ, tap water). It also works as a preposition "from" — 来自 (láizì, to come from).

Japanese: on-readings ジ (ji) and シ (shi), kun みずか.ら (mizukara). 自分 (jibun, oneself / I), 自由 (jiyū, freedom), 自然 (shizen, nature), 自転車 (jitensha, bicycle). 自分 (jibun) is one of the commonest Japanese words for "I / myself."

Korean hanja-sound "ja": 自己 (jagi, self), 自由 (jayu, freedom), 自然 (jayeon, nature), 自身 (jasin, oneself). 自然 — "being so of itself" — is a keyword of East Asian thought.

Memory aid: a nose seen from the front — the fingertip that points at "me" lands on the nose.