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

Answer:

一 -> 十 -> 土 -> 売 -> 続

一  ICHI, ITSU, hito(tsu) - one

十  JUU, tou, to - ten

土  DO, tsuchi - earth, soil

売  BAI, u(ru) - sell

続  ZOKU, tsuzu(ku) - continue