Answer:
一 -> 二 -> コ -> 口 -> 日 -> 旧 -> 田 -> 曽 -> 増
一 ICHI, ITSU, hito(tsu) - one
二 NI, futa(tsu), futa - two
コ Katakana "Ko"
口 KOU, kuchi - mouth
日 NICHI, JITSU, hi, ka - sun, day
旧 KYUU, KU - old, former
田 DEN, ta - paddy field
曽 SOU, katsute - overlap
増 ZOU, ma(su), fu(eru), fu(yasu) - increase, rise, raise