1810. This #kanjipuzzle is about evolution. Start with one character, add a few strokes, and get another, then repeat. 一 -> ? -> ? -> ? -> ? -> 曇

Answer:

一 -> 丁 -> 干 -> 雨 -> 雲 -> 曇

一  ICHI, ITSU, hito(tsu) - one

丁  CHOU, TEI - counter, block

干  KAN, hi(ru), ho(su) - get dry, dry, drink up

雨  U, ame - rain

雲  UN, kumo - cloud

曇  DON, kumo(ru) - become cloudy