2530. What character can be added to both of these characters to give other characters? 其_ -> _旦

其  shi, so - that

旦  TAN, DAN, asara, tadashi, asa - morning

Add 月:其+月 月+旦   

月  GETSU, GATSU, tsuki - moon, month

期  KI, GO - time, period, term

胆  TAN - gallbladder, courage