I was bored testing stuff, these are the crescent moon characters who get guaranteed counter hit off of a anti air 5d into 5a, the reason being all of their 5a's are active on the 4th frame.
Kohaku
Miyako
Mech Hisui
Hisui
Len
Neco Arc (yes Neco Arc)
Satsuki
Vsion
Wlen
To Double check all I did was open up training mode and test if it'll Counterhit if Nero does jump B into a double jump (if Nero Double jumps if you don't have a 4f 5a it won't be a counter hit, and depending on your 5a hitbox the j.b will beat it flat out anyway, ironically arcuied 5d 5a seemed to be netting Counterhits but didn't when Nero Double Jumped, confused me at first.)