Dia 623C can be used as an anti air. You can use Luna 623C midcombo to extend combos, such as Luna 4B > 2DD > 214D > dash 6B > 2C > 623C > dash 6DD > 2DD > air ender. Other than that, you can use it as a frame trap I guess since it does Fatal and is easy to combo after but it is hella unsafe.
Try to connect the 2DD when the green bar is around 40-45% full. Then cancel into 214D as fast as possible.