1897. What character can be added to both of these characters to give other characters? 矛_ -> _全

Answer:

一 -> 二 -> コ -> 口 -> 日 -> 目 -> 自 -> 夏

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

目  MOKU, me - eye

自  JI, SHI, mizuka(ra) - me, self

夏  KA, GE, natsu - summer