2120. What character can be added to both of these characters to give other characters? 其_ -> _巴

其  shi, so - that

巴  HE, HA, tomoe, uzumaki - spiral, whirling

Add 月:其+月 月+巴  

月  GETSU, GATSU, tsuki - moon, month

期  KI, GO - time, period, term

肥  HI, koe, ko(yashi), ko(yasu) - manure, fertilizer, grow fat