Level 65 Chen Gong still not enough to burst 2nd-Bar Kiyohime with minimal buffs after many tries. Either you'll need an NP4-5 Castoria or you have to get him reach 400% Overcharge just to deal enough damage for the next wave. Another way around is to just grail him to 90, that is if you have enough mats to invest.
CasGil is definitely replaceable here in some renditions as long as the same thing works.
#fgo
#fgona
#fategrandorder
