2720. This #kanjipuzzle is about evolution. Start with one character, add a few strokes, and get another, then repeat. 一 -> ? -> ? -> ? -> ? -> 誕

一 -> 丁 -> 工 -> 正 -> 延 -> 誕  

一  ICHI, ITSU, hito(tsu) - one

丁  CHOU, TEI - counter, block

工  KOU, KU - artisan, skill, work

正  SEI, SHOU, tada(shii), masa(ni) - correct, just, exact

延  EN, noba(su), no(biru), no(beru) - lengthen, prolong, postpone

誕  TAN - birth