2701. This #kanjipuzzle is about evolution. Start with one character, add a few strokes, and get another, then repeat. 一 -> ? -> ? -> ? -> ? -> 脚

一 -> 十 -> 土 -> 去 -> 却 -> 脚  

一  ICHI, ITSU, hito(tsu) - one

十  JUU, tou, to - ten

土  DO, tsuchi - earth, soil

去  KYO, KO, sa(ru) - leave, move away, elapse

却  KYAKU - pull back, withdraw

脚  KYAKU, KYA, ashi - leg