Flame Gem is an experience material.
To strengthen your girl by using this gem, It will cost:
- Cost = n x ★ x 【 5 + ( level -1)】 CC
- n = Number of Flame gems
Example : Tsuruno 5 ★ lvl 67
Using 4 Flame Gems ---> Cost = 4 x 5 x 【 5 + ( level -1)】= 1420 CC
It gives 100 exp , an extra x1.5 exp bonus if the girl is of type 
.